Patent US4490691A successfully refreshed from Google Patents.
US4490691A
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Compressor-expander circuits and, circuit arrangements for modifying dynamic range, for suppressing mid-frequency modulation effects and for reducing media overload
Assignee: DOLBY RAY AS TRUSTEE OF RAY DOLBY TRUST UNDER DOLBY FAMILY TRUST INSTRUMENT DATED MAY 7 1999
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Filing: 1981-09-10
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Granted: 1984-12-25
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Expires: 2001-09-10
Abstract
Abstract In a first aspect of the invention, compressor and expander circuits are arranged in series, the dynamic actions of the circuits being substantially separated with respect to level. The changing gain portions of the characteristics are staggered among the series circuits such that the resulting overall characteristic has a maximum compression or expansion ratio substantially no greater than that of any single circuit while providing more compression or expansion than for any of the circuits individually. A second aspect, referred to as "spectral skewing", effects a reduction of the influence of signals in the high and/or low frequency extremes of a signal transmission system on the action of a compressor feeding the transmission channel. Consequently, a complementary expander fed by the channel is less likely to be controlled by signals at frequencies subject to transmission channel errors. A third aspect provides an anti-saturation effect. This aspect of the invention takes advantage of the properties of dual path compressors and expanders, in which the output of the circuits at very low signal levels is provided mostly by the further path and at high levels, mostly by the main path. The disclosure also describes combinations of two or more aspects of the invention. In one particular combined embodiment, C-type noise reduction is provided. Additionally, arrangements for compressor/expander switching and B-type/C-type noise reduction switching are disclosed.
Inventors
- 👤 Ray M. Dolby
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-26 14:32
CPC Classifications
H; H03; H03G; H03G9/00; H03G9/02; H03G9/12; H03G9/18
Claims Analysis
Total Claims: 232
Claim 1
Independent Claim
193 words
A circuit for modifying the dynamic range of an input signal, comprising first circuit means with a bi-linear characteristic composed of a low level portion of substantially constant gain up to a threshold, an intermediate level portion, above the threshold, of changing gain providing a maximum compression ratio or expansion ratio, and a high level portion of substantially constant gain different from the gain of the low level portion, and at least one second circuit means, which also has a bi-linear characteristic within a frequency range common to the circuit means, in series with the first circuit means thereby to provide an overall characteristic which is also bi-linear, the intermediate level portions of the characteristics of the circuit means being staggered within a frequency range common to the circuit means such as to provide a change of gain over a wider range of intermediate input levels than for any of the circuit means individually, and an increased difference between the gains at low and high input levels, but with an overall maximum compression or expansion ratio which is substantially no greater than that of any single circuit means, by virtue of the staggering.
Claim 2
Dependent Claim
193 words
A circuit for modifying the dynamic range of an input signal, comprising first circuit means with a bi-linear characteristic composed of a low level portion of substantially constant gain up to a threshold, an intermediate level portion, above the threshold, of changing gain providing a maximum compression ratio or expansion ratio, and a high level portion of substantially constant gain different from the gain of the low level portion, and at least one second circuit means, which also has a bi-linear characteristic within a frequency range common to the circuit means, in series with the first circuit means thereby to provide an overall characteristic which is also bi-linear, the intermediate level portions of the characteristics of the circuit means being staggered within a frequency range common to the circuit means such as to provide a change of gain over a wider range of intermediate input levels than for any of the circuit means individually, and an increased difference between the gains at low and high input levels, but with an overall maximum compression or expansion ratio which is substantially no greater than that of any single circuit means, by virtue of the staggering.
Claim 3
Dependent Claim
57 words
A circuit according to claim 1 further comprising switching means for selecting the compression or expansion mode of the circuit, said switching means selectively effecting signal connections whereby each circuit means is switched to its respective compression or expansion configuration and the arrangement of series circuit means is reversed in one mode with respect to the other.
Claim 4
Dependent Claim
40 words
A circuit according to claim 1, wherein the circuit means are compressors, each establishing its own characteristic, and the thresholds are set to different values in order to stagger the intermediate level portions of the characteristics of the circuit means.
Claim 5
Dependent Claim
25 words
A circuit according to claim 3 wherein the threshold of each successive compressor circuit means is lower than the threshold of the previous circuit means.
Claim 6
Dependent Claim
25 words
A circuit according to claim 3 wherein the threshold of each successive compressor circuit means is higher than the threshold of the previous circuit means.
Claim 7
Dependent Claim
40 words
A circuit according to claim 1, wherein the circuit means are expanders, each establishing its own characteristic, and the thresholds are set to different values in order to stagger the intermediate level portions of the characteristics of the circuit means.
Claim 8
Dependent Claim
25 words
A circuit according to claim 6 wherein the threshold of each successive expander circuit means is higher than the threshold of the previous circuit means.
Claim 9
Dependent Claim
25 words
A circuit according to claim 6 wherein the threshold of each successive expander circuit means is lower than the threshold of the previous circuit means.
Claim 10
Dependent Claim
72 words
A circuit according to any of claims 1, 3 or 6 wherein the falling flank of the compression or expansion ratio of each of the circuit means overlaps the rising flank of the compression or expansion ratio of another of the circuit means to the extent that the overall compression or expansion ratio in the overlapping region does not substantially exceed the maximum compression or expansion ratio of the adjacent circuit means.
Claim 11
Dependent Claim
37 words
A circuit accordance to claim 9, wherein each of the circuit means has a maximum compression or inverse expansion ratio of substantially 2:1 and the maximum ratio for the complete circuit arrangement does not substantially exceed 2:1.
Claim 12
Dependent Claim
35 words
A circuit according to claim 9, wherein the maximum compression or inverse expansion ratio for the complete circuit arrangement does not exceed about 11/4 times the maximum ratio of any one of the circuit means.
Claim 13
Dependent Claim
35 words
A circuit according to claim 10, wherein the maximum compression or inverse expansion ratio for the complete circuit arrangement does not exceed about 11/4 times the maximum ratio of any one of the circuit means.
Claim 14
Dependent Claim
64 words
A circuit according to any of claims 1, 3 or 6, wherein at least one of the circuit means includes variable filter means providing a boost or cut in a high or low frequency region of the signal band, and responsive to signals in that region to cause the filter means corner frequency to slide in the sense narrowing the boosted or cut region.
Claim 15
Dependent Claim
39 words
A circuit according to claim 13 wherein one of the circuit means includes said variable filter means, and wherein there is one further circuit means including a plurality of band pass filters each in combination with a limiting device.
Claim 16
Dependent Claim
46 words
A circuit according to claim 13, for audio signals, wherein the or each variable filter means includes an amplifying, rectifying, and smoothing control circuit providing a control signal to a controlled impedance device of the filter means to effect the sliding of the filter corner frequency.
Claim 17
Dependent Claim
14 words
A circuit according to claim 15, wherein each circuit means includes variable filter means.
Claim 18
Dependent Claim
29 words
A circuit according to claim 16, wherein the control circuits of the variable filter means have different gains such as to establish the different thresholds of the circuit means.
Claim 19
Dependent Claim
20 words
A circuit according to claim 16 wherein the quiescent corner frequencies of the variable filter means are substantially the same.
Claim 20
Dependent Claim
35 words
A circuit according to claim 18, wherein the boost or cut is provided in a high frequency region and the quiescent corner frequencies of the variable filter means are in the region of 375 Hz.
Claim 21
Dependent Claim
23 words
A circuit according to claim 19, wherein there are two bi-linear circuit means, each having a low level gain of substantially 10 dB.
Claim 22
Dependent Claim
65 words
A circuit according to claim 20 further comprising switching means for selecting the type characteristic mode of operation of the circuit, said switching means selectively effecting signal connections whereby said two series bi-linear circuit means comprise the respective compressor or expander in a first mode of operation and a single bi-linear circuit means comprises the respective compressor or expander in a second mode of operation.
Claim 23
Dependent Claim
80 words
A circuit according to claim 21 wherein the switching means further selects the quiescent corner frequency of the variable filter means of said single bi-linear circuit means, said switching means selectively effecting signal connections whereby in said first mode of operation the quiescent corner frequency of the variable filter means is in the region of 375 Hz and in the second mode of operation the quiescent corner frequency of the variable filter means is in the region of 1500 Hz.
Claim 24
Dependent Claim
123 words
A circuit according to claim 21 wherein said variable filter means of said single bi-linear circuit means includes a variable filter and a fixed filter, and wherein the switching means further selects the corner frequency of the fixed filter and the quiescent corner frequency of the variable filter, said switching means selectively effecting signal connections whereby in said first mode of operation the corner frequency of the fixed filter and the quiescent corner frequency of the variable filter are each in the region of 375 Hz and in said second mode of operation the corner frequency of the fixed filter is in the region of 1500 Hz and the quiescent corner frequency of the variable filter is in the region of 750 Hz.
Claim 25
Dependent Claim
79 words
A circuit according to claim 23 wherein the threshold of the second bi-linear circuit means is lower than that of first bi-linear circuit means in the case of a compressor circuit and the reverse order in the case of an expander circuit and wherein said single bi-linear circuit means in said second mode of operation is the first circuit means in the case of a compressor circuit and the second compressor means in the case of the expander circuit.
Claim 26
Dependent Claim
58 words
A circuit according to claim 24 wherein each circuit means includes overshoot suppression means having a threshold level, wherein said switching means further selects the overshoot threshold level of said first bi-linear circuit means, said switching means selectively effecting signal connections whereby in said second mode of operation said overshoot threshold level is reduced by about 3 dB.
Claim 27
Dependent Claim
27 words
A circuit according to claim 16 wherein in at least one circuit means the variable filter means includes a variable filter in series with a fixed filter.
Claim 28
Dependent Claim
34 words
A circuit according to claim 26, wherein the boost or cut is provided in a high frequency region and the or each fixed filter has a corner frequency in the region of 375 Hz.
Claim 29
Dependent Claim
35 words
A circuit according to claim 27, wherein at least two circuit means have variable filter means in series with a fixed filter and that the corner frequencies of the fixed filters are substantially the same.
Claim 30
Dependent Claim
128 words
A circuit according to any of claims 1, 3 or 6, wherein at least one of the circuit means is a dual-path circuit comprising a main path which is linear with respect to dynamic range, a combining circuit in the main path, and a further path which has its input coupled to the input or output of the main path and its output coupled to the combining circuit, the further path providing a signal which, at least in an upper part of the frequency band, boosts or bucks the main path signal by way of the combining circuit, but which is so limited that, in the upper part of the input dynamic range, the further path signal is limited to a value smaller than the main path signal.
Claim 31
Dependent Claim
64 words
A circuit according to claim 1 wherein the approximate threshold level T of a given circuit means is determined by the relationship T=F-CG/(C-1), where F is the finishing point of the circuit means, whereat the intermediate level portion ends and the high level portion starts, C is the maximum compression ratio of the circuit means and G is the gain of the circuit means.
Claim 32
Dependent Claim
60 words
A circuit according to any of claims 1, 3 or 6, wherein the circuit arrangement is for modifying the dynamic range of audio signals and wherein each circuit means includes an overshoot suppressor having a threshold level, the threshold levels being staggered among the circuit means such as to provide a reduction in the overshoots of the overall circuit arrangement.
Claim 33
Dependent Claim
51 words
A circuit according to claim 31 wherein the threshold of the overshoot suppressor of each successive compressor circuit means is lower than that of the previous circuit means and that the threshold of the overshoot suppressor of each successive expander circuit means is higher than that of the previous circuit means.
Claim 34
Dependent Claim
51 words
A circuit according to claim 31, wherein the threshold of the overshoot suppressor of each successive compressor circuit means is higher than that of the previous circuit means and that the threshold of the overshoot suppressor of each successive expander circuit means is lower than that of the previous circuit means.
Claim 35
Dependent Claim
28 words
A circuit according to any of claims 1, 3 or 6, wherein there are three bi-linear circuits means, each having a low level gain of substantially 8 dB.
Claim 36
Dependent Claim
38 words
A circuit according to claim 29 further comprising frequency dependent circuit means connected in the main path of at least one dual-path circuit means for providing signal attenuation or boosting in a selected part of the frequency band.
Claim 37
Dependent Claim
26 words
A circuit according to claim 35 which, in the case of a compressor, provides signal attenuation and, in the case of an expander, provides signal boosting.
Claim 38
Dependent Claim
366 words
A noise reduction system, comprising compressor means comprising first circuit means with a bi-linear characteristic composed of a low level portion of substantially constant gain up to a threshold, an intermediate level portion, above the threshold, of changing gain providing a maximum compression ratio, and a high level portion of substantially constant gain different from the gain of the low level portion, and at least one second circuit means, which also has a bi-linear characteristic within a frequency range common to the circuit means, in series with the first circuit means thereby to provide an overall compressor characteristic which is also bi-linear, the intermediate level portions of the characteristics of the circuit means being staggered within a frequency range common to the circuit means such as to provide a change of gain over a wider range of intermediate input levels than for any of the circuit means individually, and an increased difference between the gains at low and high input levels, but with an overall maximum compression ratio which is substantially no greater than that of any single circuit means, by virtue of the staggering, and expander means including first circuit means with a bi-linear characteristic composed of a low level portion of substantially constant gain up to a threshold, an intermediate level portion, above the threshold, of changing gain providing a maximum expansion ratio, and a high level portion of substantially constant gain different from the gain of the low level portion, and at least one second circuit means, which also has a bi-linear characteristic within a frequency range common to the circuit means, in series with the first circuit means thereby to provide an overall expander characteristic which is also bi-linear, the intermediate level portions of the characteristics of the circuit means being staggered within a frequency range common to the circuit means such as to provide a change of gain over a wider range of intermediate input levels than for any of the circuit means individually, and an increased difference between the gains at low and high input levels, but with an overall maximum expansion ratio which is substantially no greater than that of any single circuit means, by virtue of the staggering.
Claim 39
Dependent Claim
366 words
A noise reduction system, comprising compressor means comprising first circuit means with a bi-linear characteristic composed of a low level portion of substantially constant gain up to a threshold, an intermediate level portion, above the threshold, of changing gain providing a maximum compression ratio, and a high level portion of substantially constant gain different from the gain of the low level portion, and at least one second circuit means, which also has a bi-linear characteristic within a frequency range common to the circuit means, in series with the first circuit means thereby to provide an overall compressor characteristic which is also bi-linear, the intermediate level portions of the characteristics of the circuit means being staggered within a frequency range common to the circuit means such as to provide a change of gain over a wider range of intermediate input levels than for any of the circuit means individually, and an increased difference between the gains at low and high input levels, but with an overall maximum compression ratio which is substantially no greater than that of any single circuit means, by virtue of the staggering, and expander means including first circuit means with a bi-linear characteristic composed of a low level portion of substantially constant gain up to a threshold, an intermediate level portion, above the threshold, of changing gain providing a maximum expansion ratio, and a high level portion of substantially constant gain different from the gain of the low level portion, and at least one second circuit means, which also has a bi-linear characteristic within a frequency range common to the circuit means, in series with the first circuit means thereby to provide an overall expander characteristic which is also bi-linear, the intermediate level portions of the characteristics of the circuit means being staggered within a frequency range common to the circuit means such as to provide a change of gain over a wider range of intermediate input levels than for any of the circuit means individually, and an increased difference between the gains at low and high input levels, but with an overall maximum expansion ratio which is substantially no greater than that of any single circuit means, by virtue of the staggering.
Claim 40
Dependent Claim
46 words
A noise reduction system according to claim 37 wherein the threshold of each successive compressor circuit means is lower than the threshold of the previous circuit means and the threshold of each successive expander circuit means is higher than the threshold of the previous circuit means.
Claim 41
Dependent Claim
46 words
A noise reduction system according to claim 37, wherein the threshold of each successive compressor circuit means is higher than the threshold of the previous circuit means and the threshold of each successive expander circuit means is lower than the threshold of the previous circuit means.
Claim 42
Dependent Claim
77 words
A noise reduction system according to any of claims 37, 38, or 39 wherein the compressor means and the expander means are the same circuit in combination with switching means for selecting the compression or expansion mode of the circuit, said switching means selectively effecting signal connections whereby each circuit means is switched to its respective compression or expansion configuration and the arrangement of series circuit means is reversed in one mode with respect to the other.
Claim 43
Dependent Claim
227 words
A noise reduction system according to claim 37 wherein at least one of the circuit means in each of the compressor means and in the expander means is a dual-path circuit each having a main path which is linear with respect to dynamic range, a combining circuit in the main path, and a further path which has its input coupled to the input or output of the main path and its output coupled to the combining circuit, the further path providing a signal which, at least in a part of the frequency band, boosts the main path signal in the compressor means and bucks the main path signal in the expander means, by way of the combining circuit, but which in each case is so limited that, in the upper part of the input dynamic range, the further path signal is limited to a value smaller than the main path signal, the combination further comprising frequency dependent means connected in the main path of at least one dual-path circuit means in each of the compressor means and the expander means for providing in the case of the compressor means, signal attenuation in at least a portion of said part of the frequency band, and, in the case of the expander means, a complementary signal boosting in at least said portion of said part of the frequency band.
Claim 44
Dependent Claim
218 words
A signal compressor for use with complex signals in a signal transmission system in which the compressed signal is applied to a transmission channel which in turn feeds an expander, wherein the relative signal amplitude response in the transmission channel between the compressor and expander is uncertain in the region of the high and/or low frequency extremes of the useful bandwidth of said complex signals applied to the compressor, said compressor having its compression controlled by control circuitry which responds to the frequency and amplitude characteristics of said complex signals, the compressor comprising filter means for skewing the spectral balance of signals in said compressor, in an abrupt manner with respect to frequency, in a frequency region in which the ear can hear signal components, if present, but in which it has a reduced sensitivity to low level noise components, to substantially reduce the influence of said high and/or low frequency extreme region components of said complex signals in controlling said control circuitry and to attenuate said high and/or low frequency extreme region components, respectively, in said compressed signal, whereby the compressor action is significantly less susceptible to the influence of complex signals beyond the abrupt roll-off frequency and adverse effects on complementarity caused by errors in amplitude response that occur between the compressor and expander are suppressed.
Claim 45
Dependent Claim
218 words
A signal compressor for use with complex signals in a signal transmission system in which the compressed signal is applied to a transmission channel which in turn feeds an expander, wherein the relative signal amplitude response in the transmission channel between the compressor and expander is uncertain in the region of the high and/or low frequency extremes of the useful bandwidth of said complex signals applied to the compressor, said compressor having its compression controlled by control circuitry which responds to the frequency and amplitude characteristics of said complex signals, the compressor comprising filter means for skewing the spectral balance of signals in said compressor, in an abrupt manner with respect to frequency, in a frequency region in which the ear can hear signal components, if present, but in which it has a reduced sensitivity to low level noise components, to substantially reduce the influence of said high and/or low frequency extreme region components of said complex signals in controlling said control circuitry and to attenuate said high and/or low frequency extreme region components, respectively, in said compressed signal, whereby the compressor action is significantly less susceptible to the influence of complex signals beyond the abrupt roll-off frequency and adverse effects on complementarity caused by errors in amplitude response that occur between the compressor and expander are suppressed.
Claim 46
Dependent Claim
39 words
A signal compressor according to claim 42 further comprising band limitation filter means for attenuating at least a portion of the frequency spectrum of signals applied to the compressor that are outside the useful bandwidth of said complex signals.
Claim 47
Dependent Claim
56 words
A signal compressor according to claim 42 wherein the compressor includes variable filter means providing a boost or cut in a high or low frequency region and wherein said control circuitry is responsive to signals in that region to cause the filter means corner frequency to slide in the sense narrowing the boosted or cut region.
Claim 48
Dependent Claim
40 words
A signal compressor according to claim 42 wherein said filter means comprises at least one band rejecting network having at least one steep drop-off with a band attenuation characteristic located to attenuate said high and/or low frequency extreme region components.
Claim 49
Dependent Claim
28 words
A signal compressor according to claim 45 wherein said at least one band rejecting network has one or more drop offs of about 12 dB/octave to 18 dB/octave.
Claim 50
Dependent Claim
25 words
A signal compressor according to claims 45 or 46, wherein said at least one network is located in the input signal path to said compressor.
Claim 51
Dependent Claim
37 words
A signal compressor according to claim 45 wherein the control circuitry includes at least one band rejecting network and further comprises at least one further band rejecting network located in the output signal path of said compressor.
Claim 52
Dependent Claim
37 words
A signal compressor according to claim 45, wherein said at least one band rejecting network comprises a low pass filter in the high frequency extreme region and/or a high pass filter in the low frequency extreme region.
Claim 53
Dependent Claim
27 words
A signal compressor according to claim 45, wherein said at least one band rejecting network comprises a notch filter in the high and/or low frequency extreme region.
Claim 54
Dependent Claim
27 words
A signal compressor according to claim 45, wherein said at least one band rejecting network comprises a shelf network in the high and/or low frequency extreme region.
Claim 55
Dependent Claim
35 words
A signal compressor according to any of claims 49, 50 or 51 wherein the band rejecting network or networks have a depth of 6-10 dB or more in said high and/or low frequency extreme regions.
Claim 56
Dependent Claim
55 words
A signal compressor according to claims 42 or 45 in combination with an expander for expanding the dynamic range of signals compressed by said signal compressor and received via a transmission channel, the expander including circuit means for boosting the attenuated high and/or low frequency extreme region components to effect a substantially flat frequency response.
Claim 57
Dependent Claim
50 words
A signal compressor and expander according to claim 15 wherein the compressor and expander each further comprise band limitation filter means for attenuating at least a portion of the frequency spectrum of signals applied to the respective compressor and expander that are outside the useful bandwidth of said complex signals.
Claim 58
Dependent Claim
100 words
A signal compressor according to claim 45 wherein the compressor has a main signal path which is linear with respect to dynamic range, a combining circuit in the main path, and a further path which has its input coupled to the input or output of the main path and its output coupled to the combining circuit, the further path providing a signal which boosts the main path signal by way of the combining circuit, but which is limited to a value smaller than the main path signal, the filter means being located only in the further path of the compressor.
Claim 59
Dependent Claim
26 words
A signal compressor according to claim 55 wherein the filter means comprises at least one network located in the input signal path of the further path.
Claim 60
Dependent Claim
53 words
A signal compressor according to claim 55 wherein the control circuitry is in said further path and wherein said at least one network comprises at least one band rejecting network included in said control circuitry and at least one further band rejecting network located in the output signal path of said further path.
Claim 61
Dependent Claim
35 words
A signal compressor according to claim 56, wherein said at least one network comprises a low pass filter in the high frequency extreme region and/or a high pass filter in the low frequency extreme region.
Claim 62
Dependent Claim
25 words
A signal compressor according to claim 56, wherein said at least one network comprises a notch filter in the high and/or low frequency extreme region.
Claim 63
Dependent Claim
25 words
A signal compressor according to claim 56, wherein said at least one network comprises a shelf network in the high and/or low frequency extreme region.
Claim 64
Dependent Claim
34 words
A signal compressor according to claim 57, wherein said band rejecting networks comprise a low pass filter in the high frequency extreme region and/or a high pass filter in the low frequency extreme region.
Claim 65
Dependent Claim
24 words
A signal compressor according to claim 57, wherein said band rejecting networks comprise a notch filter in the high and/or low frequency extreme region.
Claim 66
Dependent Claim
24 words
A signal compressor according to claim 57, wherein said band rejecting networks comprise a shelf network in the high and/or low frequency extreme region.
Claim 67
Dependent Claim
53 words
A signal compressor according to claim 56 in combination with an expander for expanding the dynamic range of signals compressed by said compressor means and received via a transmission channel, the expander including circuit means for boosting the attenuated high and/or low frequency extreme region components to effect a substantially flat frequency response.
Claim 68
Dependent Claim
53 words
A signal compressor according to claim 57 in combination with an expander for expanding the dynamic range of signals compressed by said compressor means and received via a transmission channel, the expander including circuit means for boosting the attenuated high and/or low frequency extreme region components to effect a substantially flat frequency response.
Claim 69
Dependent Claim
171 words
A signal expander for use in receiving compressed complex signals applied to a transmission channel by a compressor, wherein the relative signal amplitude response in the transmission channel between the compressor and expander is uncertain in the region of the high and/or low frequency extremes of the useful bandwidth of signals applied to the compressor, said compressor having its compression controlled by circuitry which responds to the frequency and amplitude characteristics of said complex signals, the compressor including filter means for skewing the spectral balance of signals in said compressor to substantially reduce the influence of said high and/or low frequency extreme region components in controlling said control circuitry and to attenuate said high and/or low frequency extreme region components, respectively, in said compressed signal, said expander comprising circuit means for boosting the attenuated high and/or low frequency extreme region components, respectively, to effect a substantially flat overall compressor/expander frequency response while suppressing the adverse effects on complementarity caused by errors in amplitude response that occur between the compressor and expander.
Claim 70
Dependent Claim
171 words
A signal expander for use in receiving compressed complex signals applied to a transmission channel by a compressor, wherein the relative signal amplitude response in the transmission channel between the compressor and expander is uncertain in the region of the high and/or low frequency extremes of the useful bandwidth of signals applied to the compressor, said compressor having its compression controlled by circuitry which responds to the frequency and amplitude characteristics of said complex signals, the compressor including filter means for skewing the spectral balance of signals in said compressor to substantially reduce the influence of said high and/or low frequency extreme region components in controlling said control circuitry and to attenuate said high and/or low frequency extreme region components, respectively, in said compressed signal, said expander comprising circuit means for boosting the attenuated high and/or low frequency extreme region components, respectively, to effect a substantially flat overall compressor/expander frequency response while suppressing the adverse effects on complementarity caused by errors in amplitude response that occur between the compressor and expander.
Claim 71
Dependent Claim
38 words
A signal expander according to claim 66 wherein said circuit means has a characteristic substantially complementary to that of at least one band rejecting network with one or more drop offs of about 12 dB/octave to 18 dB/octave.
Claim 72
Dependent Claim
38 words
A signal expander according to claim 66 wherein said circuit means has a characteristic substantially complementary to a low pass filter in the high frequency extreme region and/or a high pass filter in the low frequency extreme region.
Claim 73
Dependent Claim
28 words
A signal expander according to claim 66 wherein said circuit means has a characteristic substantially complementary to a notch filter in the high and/or low frequency extreme region.
Claim 74
Dependent Claim
23 words
A signal expander according to claim 66 wherein said circuit means comprises a shelf network in the high and/or low frequency extreme region.
Claim 75
Dependent Claim
39 words
A signal expander according to claim 66 further comprising band limitation filter means for attenuating at least a portion of the frequency spectrum of signals applied to the expander that are outside the useful bandwidth of said complex signals.
Claim 76
Dependent Claim
297 words
A compressor having level dependent equalization for use in a signal transmission system in which the compressed signals are applied to a transmission channel which is susceptible to high level saturation or overload effect in part of the frequency band in which the compressor compresses the dynamic range of signals, comprising a main signal path which is linear with respect to dynamic range, a combining circuit in the main path, and a further path which has its input coupled to the input or output of the main path and its output coupled to the combining circuit, the further path providing a signal which, at least in a part of the frequency band, boosts the main path signal by way of the combining circuit, but which is so limited that, in the upper part of the input dynamic range, about -10 dB to +10 dB relative to a reference level, the further path signal is limited to a value which is small relative to the main path signal, and frequency dependent circuit means connected in that portion of the main path between the combining circuit and the input or the output of the main path where the further path has its input coupled for providing in said portion of the main path and, for signals in the upper part of the input dynamic range, in the compressor characteristic at high levels a response characteristic for substantially reducing the saturation or overload effect in at least part of the frequency band in which the effect occurs and in which the further path boosts the main path signal, the overall response characteristic of said compressor for signals in said upper part of the input dynamic range being substantially the same as that of said frequency dependent circuit means response characteristic.
Claim 77
Dependent Claim
297 words
A compressor having level dependent equalization for use in a signal transmission system in which the compressed signals are applied to a transmission channel which is susceptible to high level saturation or overload effect in part of the frequency band in which the compressor compresses the dynamic range of signals, comprising a main signal path which is linear with respect to dynamic range, a combining circuit in the main path, and a further path which has its input coupled to the input or output of the main path and its output coupled to the combining circuit, the further path providing a signal which, at least in a part of the frequency band, boosts the main path signal by way of the combining circuit, but which is so limited that, in the upper part of the input dynamic range, about -10 dB to +10 dB relative to a reference level, the further path signal is limited to a value which is small relative to the main path signal, and frequency dependent circuit means connected in that portion of the main path between the combining circuit and the input or the output of the main path where the further path has its input coupled for providing in said portion of the main path and, for signals in the upper part of the input dynamic range, in the compressor characteristic at high levels a response characteristic for substantially reducing the saturation or overload effect in at least part of the frequency band in which the effect occurs and in which the further path boosts the main path signal, the overall response characteristic of said compressor for signals in said upper part of the input dynamic range being substantially the same as that of said frequency dependent circuit means response characteristic.
Claim 78
Dependent Claim
42 words
A compressor according to claim 72 wherein the compressor treats signals in the upper part of the audio frequency band, wherein the frequency dependent circuit means provides attenuation in at least a portion of said upper part of the audio frequency band.
Claim 79
Dependent Claim
45 words
An audio compressor according to claim 73 wherein the compressor also treats signals in the lower part of the audio frequency band, wherein the frequency dependent circuit means also provides attenuation in at least a portion of said lower part of the audio frequency band.
Claim 80
Dependent Claim
329 words
An expander complementary to a compressor having level dependent equalization for use in a signal transmission system in which the compressed signals are applied to a transmission channel which is susceptible to high level saturation or overload effect in part of the frequency band in which the compressor and expander alter the dynamic range of signals, the expander fed by said transmission channel comprising a main signal path which is linear with respect to dynamic range, a combining circuit in the main path, and a further path which has its input coupled to the input or output of the main path and its output coupled to the combining circuit, the further path providing a signal which, at least in a part of the frequency band, bucks the main path signal by way of the combining circuit, but which is so limited that, in the upper part of the input dynamic range, about -10 dB to +10 dB relative to a reference level, the further path signal is limited to a value which is small relative to the main path signal, and frequency dependent circuit means connected in that portion of the main path between the combining circuit and the input or the output of the main path where the further path has its input coupled for providing in said portion of the main path and, for signals in the upper part of the input dynamic range, in the expander characteristic at high levels a response characteristic substantially inverse to that required in the compressor to substantially reduce the saturation or overload effect in at least part of the frequency band in which the effect occurs and in which the further path bucks the main path signal, the overall response characteristic of said expander for signals in said upper part of the input dynamic range being substantially the same as that of said frequency dependent circuit means response characteristic in order to complement the level dependent equalization of said compressor.
Claim 81
Dependent Claim
329 words
An expander complementary to a compressor having level dependent equalization for use in a signal transmission system in which the compressed signals are applied to a transmission channel which is susceptible to high level saturation or overload effect in part of the frequency band in which the compressor and expander alter the dynamic range of signals, the expander fed by said transmission channel comprising a main signal path which is linear with respect to dynamic range, a combining circuit in the main path, and a further path which has its input coupled to the input or output of the main path and its output coupled to the combining circuit, the further path providing a signal which, at least in a part of the frequency band, bucks the main path signal by way of the combining circuit, but which is so limited that, in the upper part of the input dynamic range, about -10 dB to +10 dB relative to a reference level, the further path signal is limited to a value which is small relative to the main path signal, and frequency dependent circuit means connected in that portion of the main path between the combining circuit and the input or the output of the main path where the further path has its input coupled for providing in said portion of the main path and, for signals in the upper part of the input dynamic range, in the expander characteristic at high levels a response characteristic substantially inverse to that required in the compressor to substantially reduce the saturation or overload effect in at least part of the frequency band in which the effect occurs and in which the further path bucks the main path signal, the overall response characteristic of said expander for signals in said upper part of the input dynamic range being substantially the same as that of said frequency dependent circuit means response characteristic in order to complement the level dependent equalization of said compressor.
Claim 82
Dependent Claim
43 words
An expander according to claim 75 wherein the expander treats signals in the upper part of the audio frequency band, wherein the frequency dependent circuit means provides a boost in at least a portion of said upper part of the audio frequency band.
Claim 83
Dependent Claim
46 words
An audio expander according to claim 76 wherein the expander also treats signals in the lower part of the audio frequency band, wherein the frequency dependent circuit means also provides a boost in at least a portion of said lower part of the audio frequency band.
Claim 84
Dependent Claim
427 words
A noise reduction system comprising a compressor having level dependent equalization for use in a signal transmission system in which the compressed signals are applied to a transmission channel which is susceptible to high level saturation or overload effect in part of the frequency band in which the compressor compresses the dynamic range of signals, and a complementary expander fed by said transmission channel, each having a main signal path which is linear with respect to dynamic range, a combining circuit in the main path, and a further path which has its input coupled to the input or output of the main path and its output coupled to the combining circuit, the further path providing a signal which, at least in a part of the frequency band boosts the main path signal in the compressor, and bucks the main path signal in the expander, by way of the combining circuit, but which is in each case so limited that, in the upper part of the input dynamic range, about -10 dB to +10 dB relative to a reference level, the further path signal is limited to a value which is small relative to the main path signal, and frequency dependent circuit means connected in that portion of each main path between the combining circuit and the input or the output of the main path where the further path has its input coupled for providing in said portion of the main path in the compressor and, for signals in the upper part of the input dynamic range, in the compressor characteristic at high levels a response characteristic for substantially reducing the saturation or overload effect in at least part of the frequency band in which the effect occurs and in which the further path boosts the main path signal, the overall response characteristic of said compressor for signals in said upper part of the input dynamic range being substantially the same as that of said frequency dependent circuit means response characteristic in the compressor and for providing in said portion of the main path in the expander, and for signals in the upper part of the input dynamic range, in the expander characteristic at high levels a response characteristic substantially inverse to that of the frequency dependent circuit means in the compressor, the overall response characteristic of said expander for signals in said upper part of the input dynamic range being substantially the same as that of said frequency dependent circuit means response characteristic in the expander in order to complement the level dependent equalization of said compressor.
Claim 85
Dependent Claim
427 words
A noise reduction system comprising a compressor having level dependent equalization for use in a signal transmission system in which the compressed signals are applied to a transmission channel which is susceptible to high level saturation or overload effect in part of the frequency band in which the compressor compresses the dynamic range of signals, and a complementary expander fed by said transmission channel, each having a main signal path which is linear with respect to dynamic range, a combining circuit in the main path, and a further path which has its input coupled to the input or output of the main path and its output coupled to the combining circuit, the further path providing a signal which, at least in a part of the frequency band boosts the main path signal in the compressor, and bucks the main path signal in the expander, by way of the combining circuit, but which is in each case so limited that, in the upper part of the input dynamic range, about -10 dB to +10 dB relative to a reference level, the further path signal is limited to a value which is small relative to the main path signal, and frequency dependent circuit means connected in that portion of each main path between the combining circuit and the input or the output of the main path where the further path has its input coupled for providing in said portion of the main path in the compressor and, for signals in the upper part of the input dynamic range, in the compressor characteristic at high levels a response characteristic for substantially reducing the saturation or overload effect in at least part of the frequency band in which the effect occurs and in which the further path boosts the main path signal, the overall response characteristic of said compressor for signals in said upper part of the input dynamic range being substantially the same as that of said frequency dependent circuit means response characteristic in the compressor and for providing in said portion of the main path in the expander, and for signals in the upper part of the input dynamic range, in the expander characteristic at high levels a response characteristic substantially inverse to that of the frequency dependent circuit means in the compressor, the overall response characteristic of said expander for signals in said upper part of the input dynamic range being substantially the same as that of said frequency dependent circuit means response characteristic in the expander in order to complement the level dependent equalization of said compressor.
Claim 86
Dependent Claim
57 words
A noise reduction system according to claim 78 wherein the compressor and expander treat signals in the upper part of the audio frequency band, wherein the frequency dependent circuit means provides attenuation in the compressor and a complementary inverse boost in the expander in at least a portion of said upper part of the audio frequency band.
Claim 87
Dependent Claim
60 words
An audio noise reduction system according to claim 79 wherein the compressor and expander also treat signals in the lower part of the audio frequency band, wherein the frequency dependent circuit means also provide attenuation in the compressor and a complementary inverse boost in the expander in at least a portion of said lower part of the audio frequency band.
Claim 88
Dependent Claim
314 words
A signal compressor for use with complex signals in a signal transmission system in which the compressed signal is applied to a transmission channel which in turn feeds an expander, wherein the relative signal amplitude response in the transmission channel between the compressor and expander is uncertain in the region of the high and/or low frequency extremes of the useful bandwidth of said complex signals applied to the compressor, said compressor having its compression controlled by control circuits which respond to the frequency and amplitude characteristics of said complex signals, said compressor comprising first circuit means with a bi-linear characteristic composed of a low level portion of substantially constant gain up to a threshold, an intermediate level portion, above the threshold, of changing gain providing a maximum compression ratio or expansion ratio, and a high level portion of substantially constant gain different from the gain of the low level portion, and at least one second circuit means, which also has a bi-linear characteristic within a frequency range common to the circuit means, in series with the first circuit means, the intermediate level portions of the characteristics of the circuit means being staggered within a frequency range common to the circuit means such as to provide a change of gain over a wider range of intermediate input levels than for any of the circuit means individually, and an increased difference between the gains at low and high input levels, but with a maximum compression or expansion ratio which is substantially no greater than that of any single circuit means, by virtue of the staggering, said compressor further comprising filter means for affecting the spectral balance of signals in said compressor to substantially exclude said high and/or low frequency extreme region components of said complex signals from controlling said control circuits and to attenuate said high and/or low frequency extreme region components in said compressed signal.
Claim 89
Dependent Claim
314 words
A signal compressor for use with complex signals in a signal transmission system in which the compressed signal is applied to a transmission channel which in turn feeds an expander, wherein the relative signal amplitude response in the transmission channel between the compressor and expander is uncertain in the region of the high and/or low frequency extremes of the useful bandwidth of said complex signals applied to the compressor, said compressor having its compression controlled by control circuits which respond to the frequency and amplitude characteristics of said complex signals, said compressor comprising first circuit means with a bi-linear characteristic composed of a low level portion of substantially constant gain up to a threshold, an intermediate level portion, above the threshold, of changing gain providing a maximum compression ratio or expansion ratio, and a high level portion of substantially constant gain different from the gain of the low level portion, and at least one second circuit means, which also has a bi-linear characteristic within a frequency range common to the circuit means, in series with the first circuit means, the intermediate level portions of the characteristics of the circuit means being staggered within a frequency range common to the circuit means such as to provide a change of gain over a wider range of intermediate input levels than for any of the circuit means individually, and an increased difference between the gains at low and high input levels, but with a maximum compression or expansion ratio which is substantially no greater than that of any single circuit means, by virtue of the staggering, said compressor further comprising filter means for affecting the spectral balance of signals in said compressor to substantially exclude said high and/or low frequency extreme region components of said complex signals from controlling said control circuits and to attenuate said high and/or low frequency extreme region components in said compressed signal.
Claim 90
Dependent Claim
117 words
A signal compressor according to claim 81 wherein at least one of the circuit means is a dual-path circuit comprising a main path which is linear with respect to dynamic range, a combining circuit in the main path, and a further path which has its input coupled to the input or output of the further path and its output coupled to the combining circuit, the further path providing a signal which, at least in a part of the frequency band, boosts the main path signal by way of the combining circuit, but which is so limited that, in the upper part of the input dynamic range, the further path signal is smaller than the main path signal.
Claim 91
Dependent Claim
42 words
A signal compressor according to claim 82 further comprising frequency dependent circuit means connected in the main path of at least one dual path circuit means for providing signal attenuation in at least a portion of said part of the frequency band.
Claim 92
Dependent Claim
65 words
A signal compressor according to any of claims 81, 82 or 83 wherein at least one of the circuit means includes variable filter means providing a boost or cut in a high or low frequency region of the signal band, and responsive to signals in that region to cause the filter means corner frequency to slide in the sense narrowing the boosted or cut region.
Claim 93
Dependent Claim
47 words
A signal compressor according to claim 84, for audio signals, wherein the or each variable filter means includes an amplifying, rectifying and smoothing control circuit providing a control signal to a controlled impedance device of the filter means to effect the sliding of the filter corner frequency.
Claim 94
Dependent Claim
15 words
A signal compressor according to claim 85, wherein each circuit means includes variable filter means.
Claim 95
Dependent Claim
30 words
A signal compressor according to claim 86, wherein the control circuits of the variable filter means have different gains such as to establish the different thresholds of the circuit means.
Claim 96
Dependent Claim
21 words
A signal compressor according to claim 86 wherein the quiescent corner frequencies of the variable filter means are substantially the same.
Claim 97
Dependent Claim
36 words
A signal compressor according to claim 88, wherein the boost or cut is provided in a high frequency region and the quiescent corner frequencies of the variable filter means are in the region of 375 Hz.
Claim 98
Dependent Claim
24 words
A signal compressor according to claim 89, wherein there are two bi-linear circuit means, each having a low level gain of substantially 10 dB.
Claim 99
Dependent Claim
58 words
A signal compressor according to claim 90 further comprising switching means for selecting the type of operation of the circuit, said switching means selectively effecting signal connections whereby said two series bi-linear circuit means comprise the compressor in a first mode of operation and a single bi-linear circuit means comprises the compressor in a second mode of operation.
Claim 100
Dependent Claim
81 words
A signal compressor according to claim 91 wherein the switching means further selects the quiescent corner frequency of the variable filter means of said single bi-linear circuit means, said switching means selectively effecting signal connections whereby in said first mode of operation the quiescent course frequency of the variable filter means is in the region of 375 Hz and in the second mode of operation the quiescent corner frequency of the variable filter means is in the region of 1500 Hz.
Claim 101
Dependent Claim
124 words
A signal compressor according to claim 91 wherein said variable filter means of said single bi-linear circuit means includes a variable filter and a fixed filter, and wherein the switching means further selects the corner frequency of the fixed filter and the quiescent corner frequency of the variable filter, said switching means selectively effecting signal connections whereby in said first mode of operation the corner frequency of the fixed filter and the quiescent corner frequency of the variable filter are each in the region of 375 Hz and in said second mode of operation the corner frequency of the fixed filter is in the region of 1500 Hz and the quiescent corner frequency of the variable filter is in the region of 750 Hz.
Claim 102
Dependent Claim
44 words
A signal compressor according to claim 93 wherein the threshold of the second bi-linear circuit means is lower than that of the first bi-linear circuit means and wherein said single bi-linear circuit means in the said second mode of operation is the first circuit.
Claim 103
Dependent Claim
58 words
A circuit according to claim 94 wherein each circuit means includes overshoot suppression means having a threshold level, wherein said switching means further selects the overshoot threshold level of said first bi-linear circuit means, said switching means selectively effecting signal connections whereby in said second mode of operation said overshoot threshold level is reduced by about 3 dB.
Claim 104
Dependent Claim
28 words
A signal compressor according to claim 86 wherein in at least one circuit means the variable filter means includes a variable filter in series with a fixed filter.
Claim 105
Dependent Claim
35 words
A signal compressor according to claim 96, wherein the boost or cut is provided in a high frequency region and the or each fixed filter has a corner frequency in the region of 375 Hz.
Claim 106
Dependent Claim
29 words
A signal compressor according to any of claims 81, 82 or 83 wherein there are three bi-linear circuit means, each having a low level gain of substantially 8 dB.
Claim 107
Dependent Claim
44 words
A signal compressor according to any of claims 81, 82 or 83 wherein said filter means comprises at least one band rejecting network having at least one steep drop-off with a band attenuation characteristic located to attenuate said high and/or low frequency extreme regions.
Claim 108
Dependent Claim
28 words
A signal compressor according to claim 99 wherein said at least one band rejecting network has one or more drop offs of about 12 dB/octave to 18 dB/octave.
Claim 109
Dependent Claim
23 words
A signal compressor according to claim 99, wherein said at least one network is located in the input signal path to said compressor.
Claim 110
Dependent Claim
23 words
A signal compressor according to claim 100, wherein said at least one network is located in the input signal path to said compressor.
Claim 111
Dependent Claim
53 words
A signal compressor according to claim 99 including a control circuit responsive to the frequency and amplitude of applied signals for controlling compression, further comprising at least one band rejecting network located in said control circuit and at least one further band rejecting network located in the output signal path of said compressor.
Claim 112
Dependent Claim
53 words
A signal compressor according to claim 100 including a control circuit responsive to the frequency and amplitude of applied signals for controlling compression, further comprising at least one band rejecting network located in said control circuit and at least one further band rejecting network located in the output signal path of said compressor.
Claim 113
Dependent Claim
37 words
A signal compressor according to claim 99, wherein said at least one band rejecting network comprises a low pass filter in the high frequency extreme region and/or a high pass filter in the low frequency extreme region.
Claim 114
Dependent Claim
27 words
A signal compressor according to claim 99, wherein said at least one band rejecting network comprises a notch filter in the high and/or low frequency extreme region.
Claim 115
Dependent Claim
27 words
A signal compressor according to claim 99, wherein said at least one band rejecting network comprises a shelf network in the high and/or low frequency extreme region.
Claim 116
Dependent Claim
29 words
A signal compressor according to claim 105 wherein the band rejecting network or networks have a depth of 6-10 dB or more in said high and/or low frequency extremes.
Claim 117
Dependent Claim
29 words
A signal compressor according to claim 106 wherein the band rejecting network or networks have a depth of 6-10 dB or more in said high and/or low frequency extremes.
Claim 118
Dependent Claim
29 words
A signal compressor according to claim 107 wherein the band rejecting network or networks have a depth of 6-10 dB or more in said high and/or low frequency extremes.
Claim 119
Dependent Claim
55 words
A signal compressor according to claims 81, 82 or 83 in combination with an expander for expanding the dynamic range of signals compressed by said compressor means and received via a transmission channel, the expander comprising circuit means for boosting the attenuated high and/or low frequency extreme regions to substantially effect a flat frequency response.
Claim 120
Dependent Claim
159 words
A signal compressor and an expander according to claim 83 wherein the expander includes first circuit means with a bi-linear characteristic, and at least one second circuit means, which also has a bi-linear characteristic within a frequency range common to the circuit means, in series with the first circuit means, the intermediate level portions of the characteristics of the circuit means being staggered within a frequency range common to the circuit means such as to provide a change of gain over a wider range of intermediate input levels than for any of the circuit means individually, and an increased difference between the gains at low and high input levels, but with a maximum expansion ratio which is substantially no greater than that of any single circuit means, by virtue of the staggering, the expander further including frequency dependent circuit means connected in the main path for providing a complementary signal boost in a selected part of the frequency band.
Claim 121
Dependent Claim
91 words
A signal compressor and expander according to claim 112 wherein the compressor and expander are the same circuit in combination with switching means for selecting the compression or expansion mode of the circuit, said switching means selectively effecting signal connections whereby each circuit means is switched to its respective compression or expansion configuration, the arrangement of series circuit means is reversed in one mode with respect to the other, and the frequency dependent circuit means connected in the main path is switched from its compressor characteristic to its complementary expander characteristic.
Claim 122
Dependent Claim
100 words
A signal compressor according to claim 83 in combination with an expander for expanding the dynamic range of signals compressed by said compressor means and received via a transmission channel, wherein the expander comprises at least one dual path circuit in which the further path bucks the main path signal, the combination further comprising frequency dependent circuit means connected in the main path for providing a complementary signal boost in said selected part of the frequency band, and further circuit means for boosting the attenuated high and/or low frequency extreme regions to effect a substantially flat overall compressor/expander frequency response.
Claim 123
Dependent Claim
132 words
A signal compressor and an expander according to claim 114 wherein the expander includes first circuit means with a bi-linear characteristic, and at leaast one second circuit means, which also has a bi-linear characteristic within a frequency range common to the circuit means, in series with the first circuit means, the intermediate level portions of the characteristics of the circuit means being staggered within a frequency range common to the circuit means such as to provide a change of gain over a wider range of intermediate input levels than for any of the circuit means individually, and an increased difference between the gains at low and high input levels, but with a maximum expansion ratio which is substantially no greater than that of any single circuit means, by virtue of the staggering.
Claim 124
Dependent Claim
91 words
A signal compressor and expander according to claim 115 wherein the compressor and expander are the same circuit in combination with switching means for selecting the compression or expansion mode of the circuit, said switching means selectively effecting signal connections whereby each circuit means is switched to its respective compression or expansion configuration, the arrangement of series circuit means is reversed in one mode with respect to the other and the frequency dependent circuit means connected in the main path is switched from its compressor characteristic to its complementary expander characteristic.
Claim 125
Dependent Claim
269 words
A signal expander for use with complex signals in receiving a compressed signal applied to a transmission channel by a compressor, wherein the relative signal amplitude response in the transmission channel between the compressor and expander is uncertain in the region of the high and/or low frequency extremes of the useful bandwidth of said complex signals applied to the compressor, said compressor having its compression controlled by control circuits which respond to the frequency and amplitude characteristics of said complex signals, the compressor comprising filter means for affecting the spectral balance of signals in said compressor to substantially exclude said high and/or low frequency extreme region components from controlling said control circuits and to attenuate said high and/or low frequency extreme region components in said compressed signal, said expander comprising first circuit means with a bi-linear characteristic, and at least one second circuit means, which also has a bi-linear characteristic within a frequency range common to the circuit means, in series with the first circuit means, the intermediate level portions of the characteristics of the circuit means being staggered within a frequency range common to the circuit means such as to provide a change of gain over a wider range of intermediate input levels than for any of the circuit means individually, and an increased difference between the gains at low and high input levels, but with a maximum expansion ratio which is substantially no greater than that of any single circuit means, by virtue of the staggering, and further circuit means for boosting the attenuated high and/or low frequency extreme regions to effect a substantially flat frequency response.
Claim 126
Dependent Claim
269 words
A signal expander for use with complex signals in receiving a compressed signal applied to a transmission channel by a compressor, wherein the relative signal amplitude response in the transmission channel between the compressor and expander is uncertain in the region of the high and/or low frequency extremes of the useful bandwidth of said complex signals applied to the compressor, said compressor having its compression controlled by control circuits which respond to the frequency and amplitude characteristics of said complex signals, the compressor comprising filter means for affecting the spectral balance of signals in said compressor to substantially exclude said high and/or low frequency extreme region components from controlling said control circuits and to attenuate said high and/or low frequency extreme region components in said compressed signal, said expander comprising first circuit means with a bi-linear characteristic, and at least one second circuit means, which also has a bi-linear characteristic within a frequency range common to the circuit means, in series with the first circuit means, the intermediate level portions of the characteristics of the circuit means being staggered within a frequency range common to the circuit means such as to provide a change of gain over a wider range of intermediate input levels than for any of the circuit means individually, and an increased difference between the gains at low and high input levels, but with a maximum expansion ratio which is substantially no greater than that of any single circuit means, by virtue of the staggering, and further circuit means for boosting the attenuated high and/or low frequency extreme regions to effect a substantially flat frequency response.
Claim 127
Dependent Claim
141 words
A signal expander according to claim 117 wherein at least one of the circuit means is a dual-path circuit comprising a main path which is linear with respect to dynamic range, a combining circuit in the main path, and a further path which has its input coupled to the input or output of the further path and its output coupled to the combining circuit, the further path providing a signal which, at least in a part of the frequency band, boosts the main path signal by way of the combining circuit, but which is so limited that, in the upper part of the input dynamic range, the further path signal is smaller than the main path signal, and frequency dependent means connected in the main path for providing a signal boost in a portion of said part of the frequency band.
Claim 128
Dependent Claim
41 words
A signal expander according to claims 117 or 118 wherein said further circuit means has a characteristic substantially complementary to that of at least one band rejecting network with one or more drop offs of about 12 dB/octave to 18 dB/octave.
Claim 129
Dependent Claim
41 words
A signal expander according to claims 117 or 118 wherein said further circuit means has a characteristic substantially complementary to a low pass filter in the high frequency extreme region and/or a high pass filter in the low frequency extreme region.
Claim 130
Dependent Claim
31 words
A signal expander according to claims 117 or 118 wherein said further circuit means has a characteristic substantially complementary to a notch filter in the high and/or low frequency extreme region.
Claim 131
Dependent Claim
26 words
A signal expander according to claims 117 or 118 wherein said further circuit means comprises a shelf network in the high and/or low frequency extreme region.
Claim 132
Dependent Claim
60 words
A signal expander according to claim 118 wherein at least one of the circuit means includes variable filter means providing a boost or cut in a high or low frequency region of the signal band, and responsive to signals in that region to cause the filter means corner frequency to slide in the sense narrowing the boosted or cut region.
Claim 133
Dependent Claim
63 words
A signal expander according to claim 123, for audio signals, wherein at least one of the circuit means includes variable filter means providing a boost or cut in a high or low frequency region of the signal band, and responsive to signals in that region to cause the filter means corner frequency to slide in the sense narrowing the boosted or cut region.
Claim 134
Dependent Claim
15 words
A signal expander according to claim 124 wherein each circuit means includes variable filter means.
Claim 135
Dependent Claim
30 words
A signal expander according to claim 125 wherein the control circuits of the variable filter means have different gains such as to establish the different thresholds of the circuit means.
Claim 136
Dependent Claim
21 words
A signal expander according to claim 126 wherein the quiescent corner frequencies of the variable filter means are substantially the same.
Claim 137
Dependent Claim
36 words
A signal expander according to claim 127 wherein the boost or cut is provided in a high frequency region and the quiescent corner frequencies of the variable filter means are in the region of 375 Hz.
Claim 138
Dependent Claim
24 words
A signal expander according to claim 128 wherein there are two bi-linear circuit means, each having a low level gain of substantially 10 dB.
Claim 139
Dependent Claim
28 words
A signal expander according to claim 129 wherein in at least one circuit means the variable filter means includes a variable filter in series with a fixed filter.
Claim 140
Dependent Claim
35 words
A signal expander according to claim 130, wherein the boost or cut is provided in a high frequency region and the or each fixed filter has a corner frequency in the region of 375 Hz.
Claim 141
Dependent Claim
58 words
A signal expander according to claim 129 further comprising switching means for selecting the type of operation of the circuit, said switching means selectively effecting signal connections whereby said two series bi-linear circuit means comprise the expander in a first mode of operation and a single bi-linear circuit means comprises the expander in a second mode of operation.
Claim 142
Dependent Claim
81 words
A signal expander according to claim 132 wherein the switching means further selects the quiescent corner frequency of the variable filter means of said single bi-linear circuit means, said switching means selectively effecting signal connections whereby in said first mode of operation the quiescent corner frequency of the variable filter means is in the region of 375 Hz and in the second mode of operation the quiescent corner frequency of the variable filter means is in the region of 1500 Hz.
Claim 143
Dependent Claim
124 words
A signal expander according to claim 132 wherein said variable filter means of said single bi-linear circuit means includes a variable filter and a fixed filter, and wherein the switching means further selects the corner frequency of the fixed filter and the quiescent corner frequency of the variable filter, said switching means selectively effecting signal connections whereby in said first mode of operation the corner frequency of the fixed filter and the quiescent corner frequency of the variable filter are each in the region of 375 Hz and in said second mode of operation the corner frequency of the fixed filter is in the region of 1500 Hz and the quiescent corner frequency of the variable filter is in the region of 750 Hz.
Claim 144
Dependent Claim
45 words
A signal expander according to claim 134 wherein the threshold of the first bi-linear circuit means is lower than that of the second bi-linear circuit means and wherein said single bi-linear circuit means in the said second mode of operation is the second circuit means.
Claim 145
Dependent Claim
59 words
A signal expander according to claim 135 wherein each circuit means includes overshoot suppression means having a threshold level, wherein said switching means further selects the overshoot threshold level of said first bi-linear circuit means, said switching means selectively effecting signal connections whereby in said second mode of operation said threshold overshoot level is reduced by about 3 dB.
Claim 146
Dependent Claim
483 words
A noise reduction system, comprising a signal compressor for use with complex signals in a signal transmission system in which the compressed signal is applied to a transmission channel which in turn feeds an expander, wherein the relative signal amplitude response in the transmission channel between the compressor and expander is uncertain in the region of the high and/or low frequency extremes of the useful bandwidth of said complex signals applied to the compressor, said compressor having its compression controlled by control circuits which respond to the frequency and amplitude characteristics of said complex signals, said compressor comprising first circuit means with a bi-linear characteristic composed of a low level portion of substantially constant gain up to a threshold, an intermediate level portion, above the threshold, of changing gain providing a maximum compression ratio or expansion ratio, and a high level portion of substantially constant gain different from the gain of the low level portion, and at least one second circuit means, which also has a bi-linear characteristic within a frequency range common to the circuit means, in series with the first circuit means, the intermediate level portions of the characteristics of the circuit means being staggered within a frequency range common to the circuit means such as to provide a change of gain over a wider range of intermediate input levels than for any of the circuit means individually, and an increased difference between the gains at low and high input levels, but with a maximum compression or expansion ratio which is substantially no greater than that of any single circuit means, by virtue of the staggering, said compressor further comprising filter means for affecting the spectral balance of signals in said compressor to substantially exclude said high and/or low frequency extreme region components from controlling said control circuits and to attenuate said high and/or low frequency extreme region components in said compressed signal, and a signal expander for expanding the dynamic range of complex signals compressed by said compressor means and received via a transmission channel, the expander comprising first circuit means with a bi-linear characteristic, and at least one second circuit means, which also has a bi-linear characteristic within a frequency range common to the circuit means, in series with the first circuit means, the intermediate level portions of the characteristics of the circuit means being staggered within a frequency range common to the circuit means such as to provide a change of gain over a wider range of intermediate input levels than for any of the circuit means individually, and an increased difference between the gains at low and high input levels, but with a maximum expansion ratio which is substantially no greater than that of any single circuit means, by virtue of the staggering, the expander further comprising filter means for boosting the attenuated high and/or low frequency extreme regions to effect a substantially flat compressor/expander frequency response.
Claim 147
Dependent Claim
483 words
A noise reduction system, comprising a signal compressor for use with complex signals in a signal transmission system in which the compressed signal is applied to a transmission channel which in turn feeds an expander, wherein the relative signal amplitude response in the transmission channel between the compressor and expander is uncertain in the region of the high and/or low frequency extremes of the useful bandwidth of said complex signals applied to the compressor, said compressor having its compression controlled by control circuits which respond to the frequency and amplitude characteristics of said complex signals, said compressor comprising first circuit means with a bi-linear characteristic composed of a low level portion of substantially constant gain up to a threshold, an intermediate level portion, above the threshold, of changing gain providing a maximum compression ratio or expansion ratio, and a high level portion of substantially constant gain different from the gain of the low level portion, and at least one second circuit means, which also has a bi-linear characteristic within a frequency range common to the circuit means, in series with the first circuit means, the intermediate level portions of the characteristics of the circuit means being staggered within a frequency range common to the circuit means such as to provide a change of gain over a wider range of intermediate input levels than for any of the circuit means individually, and an increased difference between the gains at low and high input levels, but with a maximum compression or expansion ratio which is substantially no greater than that of any single circuit means, by virtue of the staggering, said compressor further comprising filter means for affecting the spectral balance of signals in said compressor to substantially exclude said high and/or low frequency extreme region components from controlling said control circuits and to attenuate said high and/or low frequency extreme region components in said compressed signal, and a signal expander for expanding the dynamic range of complex signals compressed by said compressor means and received via a transmission channel, the expander comprising first circuit means with a bi-linear characteristic, and at least one second circuit means, which also has a bi-linear characteristic within a frequency range common to the circuit means, in series with the first circuit means, the intermediate level portions of the characteristics of the circuit means being staggered within a frequency range common to the circuit means such as to provide a change of gain over a wider range of intermediate input levels than for any of the circuit means individually, and an increased difference between the gains at low and high input levels, but with a maximum expansion ratio which is substantially no greater than that of any single circuit means, by virtue of the staggering, the expander further comprising filter means for boosting the attenuated high and/or low frequency extreme regions to effect a substantially flat compressor/expander frequency response.
Claim 148
Dependent Claim
71 words
A noise reduction system according to claim 137 wherein the signal compressor and the signal expander are the same circuit in combination with switching means for selecting the compression or expansion mode of the circuit, said switching means selectively effecting signal connections whereby the circuit is switched to its respective compression or expansion configuration and the arrangement of series circuit means is reversed in one mode with respect to the other.
Claim 149
Dependent Claim
235 words
A noise reduction system according to claim 137 wherein at least one of the circuit means in the compressor is a dual-path circuit comprising a main path which is linear with respect to dynamic range, a combining circuit in the main path, and a further path which has its input coupled to the input or output of the further path and its output coupled to the combining circuit, the further path providing a signal which, at least in a part of the frequency band, boosts the main path signal by way of the combining circuit, but which is so limited that, in the upper part of the input dynamic range, the further path signal is smaller than the main path signal and wherein at least one of the circuit means in the expander is a dual-path circuit comprising a main path which is linear with respect to dynamic range, a combining circuit in the main path, and a further path which has its input coupled to the input or output of the further path and its output coupled to the combining circuit, the further path providing a signal which, at least in said part of the frequency band, bucks the main path signal by way of the combining circuit, but which is so limited that, in the upper part of the input dynamic range, the further path signal is smaller than the main path signal.
Claim 150
Dependent Claim
74 words
A noise reduction system according to claim 139 further comprising frequency dependent circuit means connected in the main path of at least one dual path circuit in the compressor and at least one dual path circuit in the expander, for providing, in the case of the compressor, signal attenuation in a selected part of the frequency band, and, in the case of the expander, signal boost in said selected part of the frequency band.
Claim 151
Dependent Claim
73 words
A noise reduction system according to claim 140 for treating signals in the upper part of the audio frequency band, wherein the frequency dependent circuit means in the compressor provides attenuation in at least a portion of said upper part of the audio frequency band and wherein the frequency dependent circuit means in the expander provides a complementary boost in at least a portion of said upper part of the audio frequency band.
Claim 152
Dependent Claim
92 words
A noise reduction system according to claim 141 wherein the signal compressor and the signal expander are the same circuit in combination with switching means for selecting the compression or expansion mode of the circuit, said switching means selectively effecting signal connections whereby the circuit is switched to its respective compression or expansion configuration, the arrangement of series circuit means is reversed in one mode with respect to the other and the frequency dependent circuit means connected in the main path is switched from its compressor characteristics to its complementary expander characteristics.
Claim 153
Dependent Claim
77 words
A noise reduction system according to any of claims 137, 139 or 140 wherein each of the circuit means in the compressor and expander includes variable filter means providing a boost, in the case of the compressor, and a cut, in the case of the expander, in a high frequency region of the signal band, and responsive to signals in that region to cause the filter to slide in the sense narrowing the boosted or cut region.
Claim 154
Dependent Claim
50 words
A noise reduction system according to claim 143 wherein there are two bi-linear circuit means, each having a low level gain of substantially 10 dB in the compressor and in the expander and wherein the quiescent corner frequencies of the variable filter means are in the region of 375 Hz.
Claim 155
Dependent Claim
67 words
A noise reduction system according to claim 144 further comprising switching means for selecting the type of operation of the compressor and expander, said switching means selectively effecting signal connections whereby said two series bi-linear circuit means comprise the respective compressor or expander in a first mode of operation and a single bi-linear circuit means comprises the respective compressor or expander in a second mode of operation.
Claim 156
Dependent Claim
82 words
A noise reduction system according to claim 145 wherein the switching means further selects the quiescent corner frequency of the variable filter means of said single bi-linear circuit means, said switching means selectively effecting signal connections whereby in said first mode of operation the quiescent corner frequency of the variable filter means is in the region of 375 Hz and in the second mode of operation the quiescent corner frequency of the variable filter means is in the region of 1500 Hz.
Claim 157
Dependent Claim
125 words
A noise reduction system according to claim 145 wherein said variable filter means of said single bi-linear circuit means includes a variable filter and a fixed filter, and wherein the switching means further selects the corner frequency of the fixed filter and the quiescent corner frequency of the variable filter, said switching means selectively effecting signal connections whereby in said first mode of operation the corner frequency of the fixed filter and the quiescent corner frequency of the variable filter are each in the region of 375 Hz and in said second mode of operation the corner frequency of the fixed filter is in the region of 1500 Hz and the quiescent corner frequency of the variable filter is in the region of 750 Hz.
Claim 158
Dependent Claim
79 words
A noise reduction system according to claim 147 wherein the threshold of the second bi-linear circuit means is lower than that of first bi-linear circuit means in the case of a compressor and the reverse order in the case of an expander and wherein said single bi-linear circuit means in said second mode of operation is the first bi-linear circuit means in the case of a compressor and the second bi-linear circuit means in the case of the expander.
Claim 159
Dependent Claim
60 words
A noise reduction system according to claim 148 wherein each circuit means includes overshoot suppression means having a threshold level, wherein said switching means further selects the overshoot threshold level of said first bi-linear circuit means, said switching means selectively effecting signal connections whereby in said second mode of operation said threshold overshoot level is reduced by about 3 dB.
Claim 160
Dependent Claim
55 words
A noise reduction system according to any of claims 37, 38, 39 or 137 wherein there are the same number of bi-linear circuit means in the compressor means and the expander means and wherein each bi-linear circuit means in the expander means is complementary to the reversed order bi-linear circuit means in the compressor means.
Claim 161
Dependent Claim
93 words
A noise reduction system according to claim 145 wherein the signal compressor and the signal expander are the same circuit in combination with further switching means for selecting the compression or expansion mode of the circuit, said switching means selectively effecting signal connections whereby the circuit is switched to its respective compression or expansion configuration, the arrangement of series circuit means is reversed in one mode with respect to the other and the frequency dependent circuit means connected in the main path is switched from its compressor characteristics to its complementary expander characteristics.
Claim 162
Dependent Claim
93 words
A noise reduction system according to claim 146 wherein the signal compressor and the signal expander are the same circuit in combination with further switching means for selecting the compression or expansion mode of the circuit, said switching means selectively effecting signal connections whereby the circuit is switched to its respective compression or expansion configuration, the arrangement of series circuit means is reversed in one mode with respect to the other and the frequency dependent circuit means connected in the main path is switched from its compressor characteristics to its complementary expander characteristics.
Claim 163
Dependent Claim
93 words
A noise reduction system according to claim 147 wherein the signal compressor and the signal expander are the same circuit in combination with further switching means for selecting the compression or expansion mode of the circuit, said switching means selectively effecting signal connections whereby the circuit is switched to its respective compression or expansion configuration, the arrangement of series circuit means is reversed in one mode with respect to the other and the frequency dependent circuit means connected in the main path is switched from its compressor characteristics to its complementary expander characteristics.
Claim 164
Dependent Claim
93 words
A noise reduction system according to claim 148 wherein the signal compressor and the signal expander are the same circuit in combination with further switching means for selecting the compression or expansion mode of the circuit, said switching means selectively effecting signal connections whereby the circuit is switched to its respective compression or expansion configuration, the arrangement of series circuit means is reversed in one mode with respect to the other and the frequency dependent circuit means connected in the main path is switched from its compressor characteristics to its complementary expander characteristics.
Claim 165
Dependent Claim
93 words
A noise reduction system according to claim 149 wherein the signal compressor and the signal expander are the same circuit in combination with further switching means for selecting the compression or expansion mode of the circuit, said switching means selectively effecting signal connections whereby the circuit is switched to its respective compression or expansion configuration, the arrangement of series circuit means is reversed in one mode with respect to the other and the frequency dependent circuit means connected in the main path is switched from its compressor characteristics to its complementary expander characteristics.
Claim 166
Dependent Claim
265 words
A signal compressor for use with complex signals in a signal transmission system in which a compressed signal is applied to a transmission channel which is in turn feeds an expander, wherein the relative signal amplitude response in the transmission channel between the compressor and expander is uncertain in the region of the high and/or low frequency extremes of the useful bandwidth of said complex signals applied to the compressor, said compressor having its compression controlled by control circuits which respond to the frequency and amplitude characteristics of said complex signals, said compressor comprising a dual-path circuit comprising a main path which is linear with respect to dynamic range, a combining circuit in the main path, and a further path which has its input coupled to the input or output of the further path and its output coupled to the combining circuit, the further path providing a signal which, at least in an upper part of the frequency band, boosts the main path signal by way of the combining circuit, but which is so limited that, in the upper part of the input dynamic range, the further path signal is smaller than the main path signal, the compressor further comprising filter means for affecting the spectral balance of signals in said compressor to substantially exclude said high and/or low frequency extreme region components from controlling said control circuits and to attenuate said high and/or low frequency extreme region components in said compressed signal and frequency dependent circuit means connected in the main path for providing signal attenuation in a selected part of the frequency band.
Claim 167
Dependent Claim
265 words
A signal compressor for use with complex signals in a signal transmission system in which a compressed signal is applied to a transmission channel which is in turn feeds an expander, wherein the relative signal amplitude response in the transmission channel between the compressor and expander is uncertain in the region of the high and/or low frequency extremes of the useful bandwidth of said complex signals applied to the compressor, said compressor having its compression controlled by control circuits which respond to the frequency and amplitude characteristics of said complex signals, said compressor comprising a dual-path circuit comprising a main path which is linear with respect to dynamic range, a combining circuit in the main path, and a further path which has its input coupled to the input or output of the further path and its output coupled to the combining circuit, the further path providing a signal which, at least in an upper part of the frequency band, boosts the main path signal by way of the combining circuit, but which is so limited that, in the upper part of the input dynamic range, the further path signal is smaller than the main path signal, the compressor further comprising filter means for affecting the spectral balance of signals in said compressor to substantially exclude said high and/or low frequency extreme region components from controlling said control circuits and to attenuate said high and/or low frequency extreme region components in said compressed signal and frequency dependent circuit means connected in the main path for providing signal attenuation in a selected part of the frequency band.
Claim 168
Dependent Claim
39 words
A signal compressor according to claim 156 wherein said filter means comprises at least one band rejecting network having at least one steep drop-off with a band attenuation characteristic located to attenuate said high and/or low frequency extreme regions.
Claim 169
Dependent Claim
28 words
A signal compressor according to claim 157 wherein said at least one band rejecting network has one or more drop offs of about 12 dB/octave to 18 dB/octave.
Claim 170
Dependent Claim
25 words
A signal compressor according to claims 157 or 158, wherein said at least one network is located in the input signal path to said compressor.
Claim 171
Dependent Claim
56 words
A signal compressor according to claims 157 or 158 including a control circuit responsive to the frequency and amplitude of applied signals for controlling compression, further comprising by at least one band rejecting network located in said control circuit and at least one further band rejecting network located in the output signal path of said compressor.
Claim 172
Dependent Claim
37 words
A signal compressor according to claim 157, wherein said at least one band rejecting network comprises a low pass filter in the high frequency extreme region and/or a high pass filter in the low frequency extreme region.
Claim 173
Dependent Claim
27 words
A signal compressor according to claim 157, wherein said at least one band rejecting network comprises a notch filter in the high and/or low frequency extreme region.
Claim 174
Dependent Claim
27 words
A signal compressor according to claim 157, wherein said at least one band rejecting network comprises a shelf network in the high and/or low frequency extreme region.
Claim 175
Dependent Claim
34 words
A signal compressor according to any of claims 161, 162 or 163 wherein the band rejecting network or networks have a depth of 6-10 dB or more in said high and/or low frequency extremes.
Claim 176
Dependent Claim
55 words
A signal compressor according to claims 157 or 158 in combination with an expander for expanding the dynamic range of signals compressed by said compressor means and received via a transmission channel, the expander comprising a circuit arrangement for boosting the attenuated high and/or low frequency extreme regions to substantially effect a flat frequency response.
Claim 177
Dependent Claim
53 words
A signal compressor and expander according to claim 165 wherein the compressor and expander are the same circuit in combination with switching means for selecting the compression or expansion mode of the circuit, said switching means selectively effecting signal connections whereby each circuit means is switched to its respective compression or expansion configuration.
Claim 178
Dependent Claim
53 words
The combination of claim 165 wherein said expander comprises a dual-path circuit in which the further path provides a signal that bucks the main path signal, the combination further comprising frequency dependent circuit means connected in the main path for providing a complementary signal boost in said selected part of the frequency band.
Claim 179
Dependent Claim
75 words
A signal compressor and expander according to claim 167 wherein the compressor and expander are the same circuit in combination with switching means for selecting the compression or expansion mode of the circuit, said switching means selectively effecting signal connections whereby each circuit means is switched to its respective compression or expansion configuration, and the frequency dependent circuit means connected in the main path is switched from its compressor characteristics to its complementary expander characteristics.
Claim 180
Dependent Claim
22 words
A signal compressor according to claims 157 or 158 wherein the filter means is located in the further path of the compressor.
Claim 181
Dependent Claim
26 words
A signal compressor according to claim 169, wherein the filter means comprises at least one network located in the input signal path of the further path.
Claim 182
Dependent Claim
64 words
A signal compressor according to claim 169 further comprising a control circuit in said further path responsive to the frequency and amplitude of applied signals for controlling compression, wherein said at least one network comprises at least one band rejecting network located in said control circuit and at least one further band rejecting network located in the output signal path of said further path.
Claim 183
Dependent Claim
35 words
A signal compressor according to claim 170, wherein said at least one network comprises a low pass filter in the high frequency extreme region and/or a high pass filter in the low frequency extreme region.
Claim 184
Dependent Claim
25 words
A signal compressor according to claim 170, wherein said at least one network comprises a notch filter in the high and/or low frequency extreme region.
Claim 185
Dependent Claim
25 words
A signal compressor according to claim 170, wherein said at least one network comprises a shelf network in the high and/or low frequency extreme region.
Claim 186
Dependent Claim
35 words
A signal compressor according to claim 171, wherein said at least one network comprises a low pass filter in the high frequency extreme region and/or a high pass filter in the low frequency extreme region.
Claim 187
Dependent Claim
25 words
A signal compressor according to claim 171, wherein said at least one network comprises a notch filter in the high and/or low frequency extreme region.
Claim 188
Dependent Claim
25 words
A signal compressor according to claim 171, wherein said at least one network comprises a shelf network in the high and/or low frequency extreme region.
Claim 189
Dependent Claim
53 words
A signal compressor according to claim 170 in combination with an expander for expanding the dynamic range of signals compressed by said compressor means and received via a transmission channel, the expander comprising a circuit arrangement for boosting the attenuated high and/or low frequency extreme regions to substantially effect a flat frequency response.
Claim 190
Dependent Claim
53 words
A signal compressor according to claim 172 in combination with an expander for expanding the dynamic range of signals compressed by said compressor means and received via a transmission channel, the expander comprising a circuit arrangement for boosting the attenuated high and/or low frequency extreme regions to substantially effect a flat frequency response.
Claim 191
Dependent Claim
296 words
A signal expander for use in receiving compressed complex signals applied to a transmission channel by a compressor, wherein the relative signal amplitude response in the transmission channel between the compressor and expander is uncertain in the region of the high and/or low frequency extremes of the useful bandwidth of complex signals applied to the compressor, said compressor having its compression controlled by control circuits which respond to frequency and amplitude level characteristics of said complex signals, the compressor including filter means for affecting the spectral balance of signals in said compressor to substantially exclude said high and/or low frequency extreme region components of said complex signals from controlling said control circuits and to attenuate said high and/or low frequency extreme region components in said compressed signal and frequency dependent circuit means for providing a level responsive signal attenuation in a selected part of the frequency band, said expander comprising a dual path circuit having a main path which is linear with respect to dynamic range, a combining circuit in the main path, and a further path which has its input connected to the input or output of the further path and its output connected to the combining circuit, the further path providing a signal which, at least in an upper part of the frequency band, boosts the main path signal by way of the combining circuit, but which is so limited that, in the upper pert of the input dynamic range, the further path signal is smaller than the main path signal, frequency dependent circuit means connected in the main path for providing a complementary signal boosting in a selected part of the frequency band, and circuit means for boosting the attenuated high and/or low frequency extreme regions to substantially effect a flat frequency response.
Claim 192
Dependent Claim
296 words
A signal expander for use in receiving compressed complex signals applied to a transmission channel by a compressor, wherein the relative signal amplitude response in the transmission channel between the compressor and expander is uncertain in the region of the high and/or low frequency extremes of the useful bandwidth of complex signals applied to the compressor, said compressor having its compression controlled by control circuits which respond to frequency and amplitude level characteristics of said complex signals, the compressor including filter means for affecting the spectral balance of signals in said compressor to substantially exclude said high and/or low frequency extreme region components of said complex signals from controlling said control circuits and to attenuate said high and/or low frequency extreme region components in said compressed signal and frequency dependent circuit means for providing a level responsive signal attenuation in a selected part of the frequency band, said expander comprising a dual path circuit having a main path which is linear with respect to dynamic range, a combining circuit in the main path, and a further path which has its input connected to the input or output of the further path and its output connected to the combining circuit, the further path providing a signal which, at least in an upper part of the frequency band, boosts the main path signal by way of the combining circuit, but which is so limited that, in the upper pert of the input dynamic range, the further path signal is smaller than the main path signal, frequency dependent circuit means connected in the main path for providing a complementary signal boosting in a selected part of the frequency band, and circuit means for boosting the attenuated high and/or low frequency extreme regions to substantially effect a flat frequency response.
Claim 193
Independent Claim
171 words
A method for modifying the dynamic range of an input signal employing series circuits each with a bi-linear characteristic within a frequency range common to the circuits thereby to provide an overall characteristic which is also bi-linear, the bi-linear characteristic composed of a low level portion of substantially constant gain up to a threshold, an intermediate level portion, above the threshold, of changing gain providing a maximum compression ratio or expansion ratio, and a high level portion of substantially constant gain different from the gain of the low level portion, comprising staggering the intermediate level portions of the characteristics of the circuits within a frequency range common to the circuits such as to provide a change of gain over a wider range of intermediate input levels than for any of the circuits individually, and an increased difference between the gains at low and high input levels, but with an overall maximum compression or expansion ratio which is substantially no greater than that of any single circuit, by virtue of the staggering.
Claim 194
Independent Claim
171 words
A method for modifying the dynamic range of an input signal employing series circuits each with a bi-linear characteristic within a frequency range common to the circuits thereby to provide an overall characteristic which is also bi-linear, the bi-linear characteristic composed of a low level portion of substantially constant gain up to a threshold, an intermediate level portion, above the threshold, of changing gain providing a maximum compression ratio or expansion ratio, and a high level portion of substantially constant gain different from the gain of the low level portion, comprising staggering the intermediate level portions of the characteristics of the circuits within a frequency range common to the circuits such as to provide a change of gain over a wider range of intermediate input levels than for any of the circuits individually, and an increased difference between the gains at low and high input levels, but with an overall maximum compression or expansion ratio which is substantially no greater than that of any single circuit, by virtue of the staggering.
Claim 195
Independent Claim
196 words
A method for use in signal compression of complex signals in a signal transmission system in which the compressed signal is applied to a transmission channel which in turn feeds an expander, wherein the relative signal amplitude response in the transmission channel between the compressor and expander is uncertain in the region of the high and/or low frequency extremes of the useful bandwidth of said complex signals applied to the compressor, said compressor having its compression controlled by control circuitry which responds to the frequency and amplitude characteristics of said complex signals, comprising skewing the spectral balance of signals in said compressor, in an abrupt manner with respect to frequency, in a frequency region in which the ear can hear signal components, if present, but in which it has reduced sensitivity to low level noise components, to substantially reduce the influence of said high and/or low frequency extreme region components of said complex signals in controlling said control circuitry and to attenuate said high and/or low frequency extreme region components, respectively, in said compressed signal, whereby the adverse effects on complementarity caused by errors in amplitude response that occur between the compressor and expander are suppressed.
Claim 196
Independent Claim
196 words
A method for use in signal compression of complex signals in a signal transmission system in which the compressed signal is applied to a transmission channel which in turn feeds an expander, wherein the relative signal amplitude response in the transmission channel between the compressor and expander is uncertain in the region of the high and/or low frequency extremes of the useful bandwidth of said complex signals applied to the compressor, said compressor having its compression controlled by control circuitry which responds to the frequency and amplitude characteristics of said complex signals, comprising skewing the spectral balance of signals in said compressor, in an abrupt manner with respect to frequency, in a frequency region in which the ear can hear signal components, if present, but in which it has reduced sensitivity to low level noise components, to substantially reduce the influence of said high and/or low frequency extreme region components of said complex signals in controlling said control circuitry and to attenuate said high and/or low frequency extreme region components, respectively, in said compressed signal, whereby the adverse effects on complementarity caused by errors in amplitude response that occur between the compressor and expander are suppressed.
Claim 197
Independent Claim
168 words
A method for use in signal expansion of received compressed complex signals applied to a transmission channel by a compressor, wherein the relative signal amplitude response in the transmission channel betweeen the compressor and expander is uncertain in the region of the high and/or low frequency extremes of the useful bandwidth of signals applied to the compressor, said compressor having its compression controlled by circuitry which responds to the frequency and amplitude characteristics of said complex signals, the compressor including filter means for skewing the spectral balance of signals in said compressor to substantially reduce the influence of said high and/or low frequency extreme region components in controlling said control circuitry and to attentuate said high and/or low frequency extreme region components, respectively, in said compressed signal, comprising boosting the attenuated high and/or low frequency extreme region components, respectively, to effect a substantially flat overall compressor/expander frequency response while suppressing the adverse effects on complementarity caused by errors in amplitude response that occur between the compressor and expander.
Claim 198
Independent Claim
168 words
A method for use in signal expansion of received compressed complex signals applied to a transmission channel by a compressor, wherein the relative signal amplitude response in the transmission channel betweeen the compressor and expander is uncertain in the region of the high and/or low frequency extremes of the useful bandwidth of signals applied to the compressor, said compressor having its compression controlled by circuitry which responds to the frequency and amplitude characteristics of said complex signals, the compressor including filter means for skewing the spectral balance of signals in said compressor to substantially reduce the influence of said high and/or low frequency extreme region components in controlling said control circuitry and to attentuate said high and/or low frequency extreme region components, respectively, in said compressed signal, comprising boosting the attenuated high and/or low frequency extreme region components, respectively, to effect a substantially flat overall compressor/expander frequency response while suppressing the adverse effects on complementarity caused by errors in amplitude response that occur between the compressor and expander.
Claim 199
Independent Claim
307 words
A method for use in a compressor to provide level dependent equalization where the compressor is used in a signal transmission system in which the compressed signals are applied to a transmission channel which is susceptible to high level saturation or overload effect in part of the frequency band in which the compressor compresses the dynamic range of signals, the compressor having a main signal path which is linear with respect to dynamic range, a combining circuit in the main path, and a further path which has its input coupled to the input or output of the main path and its output coupled to the combining circuit, the further path providing a signal which, at least in part of the frequency band, boosts the main path signal by way of the combining circuit, but which is so limited that, in the upper part of the input dynamic range, about -10 dB to +10 dB relative to a reference level, the further path signal is limited to a value which is small relative to the main path signal, comprising frequency dependently attenuating the signal amplitude in that portion of the main path between the combining circuit and the input or the output of the main path where the further path has its input coupled to provide in said portion of the main path and, for signals in the upper part of the input dynamic range, in the compressor characteristic at high levels a response characteristic for substantially reducing the satuation or overload effect in at least part of the frequency band in which the effect occurs and in which the further path boosts the main path signal, the overall response characteristic of said compressor for signals in said upper part of the input dynamic range being substantially the same as that of said frequency dependently attenuating response characteristic.
Claim 200
Independent Claim
307 words
A method for use in a compressor to provide level dependent equalization where the compressor is used in a signal transmission system in which the compressed signals are applied to a transmission channel which is susceptible to high level saturation or overload effect in part of the frequency band in which the compressor compresses the dynamic range of signals, the compressor having a main signal path which is linear with respect to dynamic range, a combining circuit in the main path, and a further path which has its input coupled to the input or output of the main path and its output coupled to the combining circuit, the further path providing a signal which, at least in part of the frequency band, boosts the main path signal by way of the combining circuit, but which is so limited that, in the upper part of the input dynamic range, about -10 dB to +10 dB relative to a reference level, the further path signal is limited to a value which is small relative to the main path signal, comprising frequency dependently attenuating the signal amplitude in that portion of the main path between the combining circuit and the input or the output of the main path where the further path has its input coupled to provide in said portion of the main path and, for signals in the upper part of the input dynamic range, in the compressor characteristic at high levels a response characteristic for substantially reducing the satuation or overload effect in at least part of the frequency band in which the effect occurs and in which the further path boosts the main path signal, the overall response characteristic of said compressor for signals in said upper part of the input dynamic range being substantially the same as that of said frequency dependently attenuating response characteristic.
Claim 201
Independent Claim
335 words
A method for use in an expander complementary to a compressor having level dependent equalization where the compressor and expander are used in a signal transmission system in which the compressed signals are applied to a transmission channel which is susceptible to high level saturation or overload effect in part of the frequency band in which the compressor and expander alter the dynamic range of signals, the expander fed by said transmission channel having a main signal path which is linear with respect to dynamic range, a combining circuit in the main path, and a further path which has its input coupled to the input or output of the main path and its output coupled to the combining circuit, the further path providing a signal which, at least in a part of the frequency band, bucks the main path signal by way of the combining circuit, but which is so limited that, in the upper part of the input dynamic range, about -10 dB to +10 dB relative to a reference level, the further path signal is limited to a value smaller than the main path signal, comprising frequency dependently boosting the signal amplitude in that portion of the main path between the combining circuit and the input or the output of the main path where the further path has its input coupled to provide in said portion of the main path, and for signals in the upper part of the input dynamic range, in the expander characteristic at high levels a response characteristic inverse to that required in the compressor to substantially reduce the saturation or overload effect in at least part of the frequency band in which the effect occurs and in which the further path bucks the main path signal, the overall response characteristic of said expander for signals in said upper part of the input dynamic range being substantially the same as that of said frequency dependently boosting response characteristic in order to complement the level dependent equalization of said compressor.
Claim 202
Independent Claim
335 words
A method for use in an expander complementary to a compressor having level dependent equalization where the compressor and expander are used in a signal transmission system in which the compressed signals are applied to a transmission channel which is susceptible to high level saturation or overload effect in part of the frequency band in which the compressor and expander alter the dynamic range of signals, the expander fed by said transmission channel having a main signal path which is linear with respect to dynamic range, a combining circuit in the main path, and a further path which has its input coupled to the input or output of the main path and its output coupled to the combining circuit, the further path providing a signal which, at least in a part of the frequency band, bucks the main path signal by way of the combining circuit, but which is so limited that, in the upper part of the input dynamic range, about -10 dB to +10 dB relative to a reference level, the further path signal is limited to a value smaller than the main path signal, comprising frequency dependently boosting the signal amplitude in that portion of the main path between the combining circuit and the input or the output of the main path where the further path has its input coupled to provide in said portion of the main path, and for signals in the upper part of the input dynamic range, in the expander characteristic at high levels a response characteristic inverse to that required in the compressor to substantially reduce the saturation or overload effect in at least part of the frequency band in which the effect occurs and in which the further path bucks the main path signal, the overall response characteristic of said expander for signals in said upper part of the input dynamic range being substantially the same as that of said frequency dependently boosting response characteristic in order to complement the level dependent equalization of said compressor.
Claim 203
Independent Claim
459 words
A method for use in a noise reduction system comprising a compressor having level dependent equalization for use in a signal transmission system in which the compressed signals are applied to a transmission channel which is susceptible to high level saturation or overload effect in part of the frequency band in which the compressor compresses the dynamic range of signals, and a complementary expander fed by said transmission channel, each having a main signal path which is linear with respect to dynamic range, a combining circuit in the main path, and a further path which has its input coupled to the input or output of the main path and its output coupled to the combining circuit, the further path providing a signal which, at least in a part of the frequency band boosts the main path signal in the compressor, and bucks the main path signal in the expander, by way of the combining circuit, but which is in each case so limited that, in the upper part of the input dyanmic range, about -10 dB to +10 dB relative to a reference level, the further path signal is limited to a value which is small relative to the main path signal, comprising frequency dependently attenuating the signal amplitude in that portion of the main path between the combining circuit and the input or the output of the main path where the further path has its input coupled in the compressor to provide in said portion of the compressor main path and, for signals in the upper part of the input dynamic range, in the compressor characteristic at high levels a response characteristic for substantially reducing the saturation or overload effect in at least part of the frequency band in which the effect occurs and in which the further path boosts the main path signal, the overall response characteristic of said compressor in said upper part of the input dynamic range being substantially the same as that of said frequency dependently attenuating response characteristic and complementarily boosting the signal amplitude in that portion of the main path between the combining circuit and the input or the output of the main path where the further path has its input coupled in the expander to provide in said portion of the expander main path, and for signals in the upper part of the input dynamic range, in the expander characteristic at high levels a response characteristic inverse to that of the frequency dependently attenuating response characteristic in the compressor, the overall response characteristic of said expander for signals in said upper part of the input dynamic range being substantially the same as that of said frequency dependently boosting response characteristic in order to complement the level dependent equalization of said compressor.
Claim 204
Independent Claim
459 words
A method for use in a noise reduction system comprising a compressor having level dependent equalization for use in a signal transmission system in which the compressed signals are applied to a transmission channel which is susceptible to high level saturation or overload effect in part of the frequency band in which the compressor compresses the dynamic range of signals, and a complementary expander fed by said transmission channel, each having a main signal path which is linear with respect to dynamic range, a combining circuit in the main path, and a further path which has its input coupled to the input or output of the main path and its output coupled to the combining circuit, the further path providing a signal which, at least in a part of the frequency band boosts the main path signal in the compressor, and bucks the main path signal in the expander, by way of the combining circuit, but which is in each case so limited that, in the upper part of the input dyanmic range, about -10 dB to +10 dB relative to a reference level, the further path signal is limited to a value which is small relative to the main path signal, comprising frequency dependently attenuating the signal amplitude in that portion of the main path between the combining circuit and the input or the output of the main path where the further path has its input coupled in the compressor to provide in said portion of the compressor main path and, for signals in the upper part of the input dynamic range, in the compressor characteristic at high levels a response characteristic for substantially reducing the saturation or overload effect in at least part of the frequency band in which the effect occurs and in which the further path boosts the main path signal, the overall response characteristic of said compressor in said upper part of the input dynamic range being substantially the same as that of said frequency dependently attenuating response characteristic and complementarily boosting the signal amplitude in that portion of the main path between the combining circuit and the input or the output of the main path where the further path has its input coupled in the expander to provide in said portion of the expander main path, and for signals in the upper part of the input dynamic range, in the expander characteristic at high levels a response characteristic inverse to that of the frequency dependently attenuating response characteristic in the compressor, the overall response characteristic of said expander for signals in said upper part of the input dynamic range being substantially the same as that of said frequency dependently boosting response characteristic in order to complement the level dependent equalization of said compressor.
Claim 205
Independent Claim
187 words
A method for treating an input signal x to provide an output signal z comprising the steps of: operating linearly upon said input signal to provide a first signal component proportional to F AS x, where F AS is a linear operator, operating non-linearly upon said input signal to provide a second signal component F 1 F AS y where F 1 is a non-linear operator decreasing as y increases, combining said first and second signal components additively to provide an intermediate signal y=F AS x+F 1 F AS y, transmitting and receiving or recording and playing back said intermediate signal, operating linearly upon said intermediate signal as received or played back to provide a third signal component proportional to yF' AS , where F' AS is a linear operator substantially the reciprocal of F AS , operating non-linearly upon said output signal to provide a fourth signal component F 2 y where F 2 is a non-linear operator at least substantially the same as F 1 , and combining said third and fourth signal components subtractively to provide said output signal z=F'.sub.AS y-F.sub.2 y whereby ##EQU5##
Claim 206
Independent Claim
187 words
A method for treating an input signal x to provide an output signal z comprising the steps of: operating linearly upon said input signal to provide a first signal component proportional to F AS x, where F AS is a linear operator, operating non-linearly upon said input signal to provide a second signal component F 1 F AS y where F 1 is a non-linear operator decreasing as y increases, combining said first and second signal components additively to provide an intermediate signal y=F AS x+F 1 F AS y, transmitting and receiving or recording and playing back said intermediate signal, operating linearly upon said intermediate signal as received or played back to provide a third signal component proportional to yF' AS , where F' AS is a linear operator substantially the reciprocal of F AS , operating non-linearly upon said output signal to provide a fourth signal component F 2 y where F 2 is a non-linear operator at least substantially the same as F 1 , and combining said third and fourth signal components subtractively to provide said output signal z=F'.sub.AS y-F.sub.2 y whereby ##EQU5##
Claim 207
Dependent Claim
177 words
A compressor for compressing the dynamic range of signals applied to a transmission channel, the channel being subject to saturation or overload effect within the range of frequencies in which the compressor compresses the dynamic range of signals, comprising a main signal path which is linear with respect to dynamic range, a combining circuit in the main path; and a further path which has its input coupled to the input or output of the main path and its output coupled to the combining circuit, the further path providing a signal which, at least in a part of the frequency band, boosts the main path signal by way of the combining circuit, but which is so limited that, in the upper part of the input dynamic range, the further path signal is limited to a value smaller than the main path signal, and frequency dependent circuit means connected in the main path for providing a reduction in frequency response in the part of the frequency band in which the transmission channel is subject to saturation or overload effect.
Claim 208
Dependent Claim
177 words
A compressor for compressing the dynamic range of signals applied to a transmission channel, the channel being subject to saturation or overload effect within the range of frequencies in which the compressor compresses the dynamic range of signals, comprising a main signal path which is linear with respect to dynamic range, a combining circuit in the main path; and a further path which has its input coupled to the input or output of the main path and its output coupled to the combining circuit, the further path providing a signal which, at least in a part of the frequency band, boosts the main path signal by way of the combining circuit, but which is so limited that, in the upper part of the input dynamic range, the further path signal is limited to a value smaller than the main path signal, and frequency dependent circuit means connected in the main path for providing a reduction in frequency response in the part of the frequency band in which the transmission channel is subject to saturation or overload effect.
Claim 209
Dependent Claim
78 words
A compressor according to claim 188 wherein the signals lie in the audio frequency band and the transmission channel is subject to saturation or overload effect beginning at a frequency in the upper part of the frequency band, where the upper part of the frequency band is from about 300 Hz upwards, wherein the frequency dependent circuit means provides a reduction in frequency response in the range upwards from the frequency where the saturation or overload effect begins.
Claim 210
Dependent Claim
76 words
A compressor according to claim 189 which also acts at low frequencies, and the transmission channel is subject to saturation or overload effect beginning at a frequency in the lower part of the frequency band, where the lower part of the frequency band is from about 100 Hz downward, wherein the frequency dependent circuit means also provides a reduction in frequency response in the range downward from the frequency where the saturation or overload effect begins.
Claim 211
Dependent Claim
220 words
An expander for expanding the dynamic range of a compressed signal received from a transmission channel fed by a compressor, the transmission channel being subject to saturation or overload effect within the range of frequencies in which the compressor and expander alter the dynamic range of signals, the compressor having a frequency dependent circuit for reducing the frequency response of signals in the part of the frequency band in which the transmission channel is subject to saturation or overload effect, the expander comprising a main signal path which is linear with respect to dynamic range, a combining circuit in the main path, and a further path which has its input coupled to the input or output of the main path and its output coupled to the combining circuit, the further path providing a signal which, at least in a part of the frequency band, bucks the main path signal by way of the combining circuit, but which is so limited that, in the upper part of the input dynamic range, the further path signal is limited to a value smaller than the main path signal, and frequency dependent circuit means connected in the main path for providing an increased frequency response in said part of the frequency band in which the transmission channel is subject to saturation or overload effect.
Claim 212
Dependent Claim
220 words
An expander for expanding the dynamic range of a compressed signal received from a transmission channel fed by a compressor, the transmission channel being subject to saturation or overload effect within the range of frequencies in which the compressor and expander alter the dynamic range of signals, the compressor having a frequency dependent circuit for reducing the frequency response of signals in the part of the frequency band in which the transmission channel is subject to saturation or overload effect, the expander comprising a main signal path which is linear with respect to dynamic range, a combining circuit in the main path, and a further path which has its input coupled to the input or output of the main path and its output coupled to the combining circuit, the further path providing a signal which, at least in a part of the frequency band, bucks the main path signal by way of the combining circuit, but which is so limited that, in the upper part of the input dynamic range, the further path signal is limited to a value smaller than the main path signal, and frequency dependent circuit means connected in the main path for providing an increased frequency response in said part of the frequency band in which the transmission channel is subject to saturation or overload effect.
Claim 213
Dependent Claim
78 words
An expander according to claim 191 wherein the signals lie in the audio frequency band and the transmission channel is subject to saturation or overload effect beginning at a frequency in the upper part of the frequency band, where the upper part of the frequency band is from about 300 Hz upwards, wherein the frequency dependent circuit means provides an increase in frequency response in the range upwards from the frequency where the saturation or overload effect begins.
Claim 214
Dependent Claim
76 words
An expander according to claim 192 which also acts at low frequencies, and the transmission channel is subject to saturation or overload effect beginning at a frequency in the lower part of the frequency band, where the lower part of the frequency band is from about 100 Hz downward, wherein the frequency dependent circuit means also provides an increase in frequency response in the range downward from the frequency where the saturation or overload effect begins.
Claim 215
Dependent Claim
215 words
A noise reduction system comprising a compressor for compressing the dynamic range of signals applied to a transmission channel, the channel being subject to saturation or overload effect within the range of frequencies in which the compressor compresses the dynamic range of signals, and an expander for expanding the dynamic range of signals received from said transmission channel, the compressor and expander each having a main signal path which is linear with respect to dynamic range, a combining circuit in the main path, and a further path which has its input coupled to the input or output of the main path and its output coupled to the combining circuit, the further path providing a signal which, at least in a part of the frequency band, bucks the main path signal by way of the combining circuit, but which is so limited that, in the upper part of the input dynamic range, the further path signal is limited to a value smaller than the main path signal, and frequency dependent circuit means connected in the main paths for providing a reduction in frequency response in the compressor and a complementary increase in frequency response in the expander in said part of the frequency band in which the transmission channel is subject to saturation or overload effect.
Claim 216
Dependent Claim
215 words
A noise reduction system comprising a compressor for compressing the dynamic range of signals applied to a transmission channel, the channel being subject to saturation or overload effect within the range of frequencies in which the compressor compresses the dynamic range of signals, and an expander for expanding the dynamic range of signals received from said transmission channel, the compressor and expander each having a main signal path which is linear with respect to dynamic range, a combining circuit in the main path, and a further path which has its input coupled to the input or output of the main path and its output coupled to the combining circuit, the further path providing a signal which, at least in a part of the frequency band, bucks the main path signal by way of the combining circuit, but which is so limited that, in the upper part of the input dynamic range, the further path signal is limited to a value smaller than the main path signal, and frequency dependent circuit means connected in the main paths for providing a reduction in frequency response in the compressor and a complementary increase in frequency response in the expander in said part of the frequency band in which the transmission channel is subject to saturation or overload effect.
Claim 217
Dependent Claim
104 words
A noise reduction system according to claim 194 wherein the signals lie in the audio frequency band and the transmission channel is subject to saturation or overload effect beginning at a frequency in the upper part of the frequency band, where the upper part of the frequency band is from about 300 Hz upwards, wherein in the compressor the frequency dependent circuit means provides a reduction in frequency response in the range upwards from the frequency where the saturation or overload effect begins, and in the expander, respectively, the frequency dependent circuit means provides an increase in the frequency response in the same range.
Claim 218
Dependent Claim
102 words
A noise reduction system according to claim 195 which also acts at low frequencies, and the transmission channel is subject to saturation or overload effect beginning at a frequency in the lower part of the frequency band, where the lower part of the frequency band is from about 100 Hz downward, wherein the frequency dependent circuit means in the compressor also provides a reduction in frequency response in the range downward from the frequency where the saturation or overload effect begins and in the expander, respectively, the frequency dependent circuit means also produces an increase in frequency response in the same range.
Claim 219
Dependent Claim
76 words
A noise reduction system according to claims 78 or 194 wherein the compressor and expander are the same circuit in combination with switching means for selecting the compression or expansion mode of the circuit, said switching means selectively effecting signal connections whereby the circuit is switched to its respective compression or expansion configuration and the frequency dependent circuit means connected in the main path is switched from its compressor characteristic to its complementary inverse expander characteristic.
Claim 220
Dependent Claim
148 words
A circuit for modifying the dynamic range of an input signal, comprising first circuit means having a characteristic in which only a portion thereof has a changing gain between low and high input levels and at least one second circuit means which also has such a characteristic within a frequency range common to the circuit means, in series with the first circuit means, the changing gain portions of the characteristics of the circuit means being staggered within a frequency range common to the circuit means such as to provide a change of gain over a wider range of input levels than for any one of the circuit means individually, and an increased difference between the gains at low and high input levels, but with a maximum overall compression or expansion ratio which is substantially no greater than that of any single circuit means, by virtue of the staggering.
Claim 221
Dependent Claim
148 words
A circuit for modifying the dynamic range of an input signal, comprising first circuit means having a characteristic in which only a portion thereof has a changing gain between low and high input levels and at least one second circuit means which also has such a characteristic within a frequency range common to the circuit means, in series with the first circuit means, the changing gain portions of the characteristics of the circuit means being staggered within a frequency range common to the circuit means such as to provide a change of gain over a wider range of input levels than for any one of the circuit means individually, and an increased difference between the gains at low and high input levels, but with a maximum overall compression or expansion ratio which is substantially no greater than that of any single circuit means, by virtue of the staggering.
Claim 222
Dependent Claim
57 words
A circuit according to claim 198 further comprising switching means for selecting the compression or expansion mode of the circuit, said switching means selectively effecting signal connections whereby each circuit means is switched to its respective compression or expansion configuration and the arrangement of series circuit means is reversed in one mode with respect to the othes.
Claim 223
Dependent Claim
49 words
A circuit according to claim 198 in which the transition region between portions of the circuit means characteristic as the input level rises from low levels is the threshold, wherein the thresholds are set to different values in order to stagger the changing gain portions of the circuit means.
Claim 224
Dependent Claim
19 words
A circuit according to claims 198 or 200 wherein the circuit means are compressors, each establishing its own characteristic.
Claim 225
Dependent Claim
25 words
A circuit according to claim 201 wherein the threshold of each successive compressor circuit means is lower than the threshold of the previous circuit means.
Claim 226
Dependent Claim
25 words
A circuit according to claim 201 wherein the threshold of each successive compressor circuit means is higher than the threshold of the previous circuit means.
Claim 227
Dependent Claim
19 words
A circuit according to claims 198 or 200 wherein the circuit means are expanders, each establishing its own characteristic.
Claim 228
Dependent Claim
25 words
A circuit according to claim 204 wherein the threshold of each successive expander circuit means is higher than the threshold of the previous circuit means.
Claim 229
Dependent Claim
25 words
A circuit according to claim 204 wherein the threshold of each successive expander circuit means is lower than the threshold of the previous circuit means.
Claim 230
Dependent Claim
69 words
A circuit according to claims 198 or 200 wherein the falling flank of the compression or expansion ratio of each of the circuit means overlaps the rising flank of the compression or expansion ratio of another of the circuit means to the extent that the overall compression or expansion ratio in the overlapping region does not substantially exceed the maximum compression or expansion ratio of the adjacent circuit means.
Claim 231
Independent Claim
184 words
A method of treating an input signal x to provide an output signal z comprising the steps of: operating linearly upon said input signal to provide a first signal component proportional to F AS x, where F AS is a linear operator, operating non-linearly upon said input signal to provide a second signal component F 1 x where F 1 is a non-linear operator decreasing as x increases, combining said first and second signal components additively to provide an intermediate signal y=(F AS +F 1 )x, transmitting and receiving or recording and playing back said intermediate signal, operating linearly upon said intermediate signal as received or played back to provide a third signal component proportional to yF' AS , where F' AS is a linear operator substantially the reciprocal of F AS , operating non-linearly upon said output signal to provide a fourth signal component zF 2 F' AS where F 2 is a non-linear operator at least substantially the same as F 1 , and combining said third and fourth signal components subtractively to provide said output signal z=yF'.sub.AS -zF.sub.2 F'.sub.AS whereby ##EQU6##
Claim 232
Independent Claim
184 words
A method of treating an input signal x to provide an output signal z comprising the steps of: operating linearly upon said input signal to provide a first signal component proportional to F AS x, where F AS is a linear operator, operating non-linearly upon said input signal to provide a second signal component F 1 x where F 1 is a non-linear operator decreasing as x increases, combining said first and second signal components additively to provide an intermediate signal y=(F AS +F 1 )x, transmitting and receiving or recording and playing back said intermediate signal, operating linearly upon said intermediate signal as received or played back to provide a third signal component proportional to yF' AS , where F' AS is a linear operator substantially the reciprocal of F AS , operating non-linearly upon said output signal to provide a fourth signal component zF 2 F' AS where F 2 is a non-linear operator at least substantially the same as F 1 , and combining said third and fourth signal components subtractively to provide said output signal z=yF'.sub.AS -zF.sub.2 F'.sub.AS whereby ##EQU6##
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USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1987-12-25 | 1988-06-25 | 1988-12-25 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1991-12-25 | 1992-06-25 | 1992-12-25 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1995-12-25 | 1996-06-25 | 1996-12-25 | $7700.00 | Window Closed / Lapsed |