US3631365A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Signal compressors and expanders
Assignee: Dolby Laboratories Inc
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Filing: 1969-10-20
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Granted: 1971-12-28
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Expires: 1989-10-20
Abstract
Abstract Signal compressor or expander action is obtained by passing the signal through a main path which provides an undistorted signal. A further path is tapped off the main path and amplifies and limits the signal. The output of the further path is used to boost or buck the signal in the main path to obtain compressor or expander action. This action takes place in a restricted frequency band defined by a variable filter in the further path, this filter being responsive to the output of the further path to narrow the pass band when this output increases. The filter comprises two filters in cascade, a fixed value filter and a variable filter which includes a voltage-controlled variable resistance. The two filters can be simple RC filters but in combination they give a 12dB/octave cutoff which is important in avoiding noise modulation effects. Various advantageous filter configurations are disclosed.
Inventors
- 👤 Ray M Dolby
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-24 09:36
CPC Classifications
H; H03; H03G; H03G9/00; H03G9/02; H03G9/025; H03G9/12; H03G9/18; H04; H04B; H04B1/00; H04B1/62; H04B1/64
Claims Analysis
Total Claims: 30
Claim 1
Independent Claim
316 words
A signal processing system for producing an output signal in response to an input signal comprising a main signal path responsive to said input signal and including means for providing in a specified frequency band extending between first and second limits a first signal substantially proportional to said input signal; a further signal path coupled to said main signal path and responsive to a signal derived from said main signal path for producing a second signal in said specified frequency band, and signal combining means for combining said first and second signals to produce said output signal, said further signal path including a first filter having fixed value components for providing pass characteristics in a fixed band extending from said first limit to a cutoff frequency intermediate said first limit and said second limit; and means for limiting the amplitude of the output signal of the further signal path; said means including a second filter connected in cascade with said first filter and having variable cutoff characteristics, said second filter including a variable impedance means responsive to an increase in the amplitude of at least one of the output of and the input to said further signal path for altering said cutoff characteristics from wide band pass under very low input signal conditions To progressively narrower band pass, providing a cutoff frequency which shifts away from said second limit sufficiently to attenuate, in combination with the said characteristics of said first filter, any high-level input signal components at any given frequency in said specified frequency band to a specified level corresponding in said second signal to a small fractional part of the maximum level of said input signal, while permitting input signal components below said specified level at frequencies nearer to said first limit then said given frequency to pass through said filters and to appear in said second signal with a lesser degree of attenuation.
Claim 2
Dependent Claim
316 words
A signal processing system for producing an output signal in response to an input signal comprising a main signal path responsive to said input signal and including means for providing in a specified frequency band extending between first and second limits a first signal substantially proportional to said input signal; a further signal path coupled to said main signal path and responsive to a signal derived from said main signal path for producing a second signal in said specified frequency band, and signal combining means for combining said first and second signals to produce said output signal, said further signal path including a first filter having fixed value components for providing pass characteristics in a fixed band extending from said first limit to a cutoff frequency intermediate said first limit and said second limit; and means for limiting the amplitude of the output signal of the further signal path; said means including a second filter connected in cascade with said first filter and having variable cutoff characteristics, said second filter including a variable impedance means responsive to an increase in the amplitude of at least one of the output of and the input to said further signal path for altering said cutoff characteristics from wide band pass under very low input signal conditions To progressively narrower band pass, providing a cutoff frequency which shifts away from said second limit sufficiently to attenuate, in combination with the said characteristics of said first filter, any high-level input signal components at any given frequency in said specified frequency band to a specified level corresponding in said second signal to a small fractional part of the maximum level of said input signal, while permitting input signal components below said specified level at frequencies nearer to said first limit then said given frequency to pass through said filters and to appear in said second signal with a lesser degree of attenuation.
Claim 3
Dependent Claim
18 words
A signal processing system according to claim 1 wherein the variable impedance means is a field effect transistor.
Claim 4
Dependent Claim
18 words
A signal processing system according to claim 1 wherein the first filter is a single section RC filter.
Claim 5
Dependent Claim
34 words
A signal processing system according to claim 1 wherein the second filter comprises a series arm consisting of a capacitor in parallel with a resistor and a shunt arm comprising a variable resistance device.
Claim 6
Dependent Claim
32 words
A signal processing system according to claim 1 wherein the second filter includes a series capacitor followed by a shunt resistor followed by a further shunt arm comprising a variable resistance device.
Claim 7
Dependent Claim
16 words
A filter according to claim 4 wherein the variable resistance device is a field effect transistor.
Claim 8
Dependent Claim
16 words
A filter according to claim 5 wherein the variable resistance device is a field effect transistor.
Claim 9
Dependent Claim
31 words
A signal processing system according to claim 1 wherein said signal combining means additively combines said first signal and said second signal, whereby said signal processing system operates as a compressor.
Claim 10
Dependent Claim
30 words
A signal processing system according to claim 1 wherein said signal combining means subtractively combines said first and said second signals whereby said signal processing system operates as an expander.
Claim 11
Dependent Claim
19 words
A signal processing system according to claim 8 wherein said further signal path is responsive to said input signal.
Claim 12
Dependent Claim
18 words
A signal processing system according to claim 8 wherein said further signal is responsive to said output signal.
Claim 13
Dependent Claim
19 words
A signal processing system according to claim 9 wherein said further signal path is responsive to said input signal.
Claim 14
Dependent Claim
19 words
A signal processing system according to claim 9 wherein said further signal path is responsive to said output signal.
Claim 15
Dependent Claim
35 words
A signal processing system according to claim 1 wherein said further signal path further comprises a nonlinear limiter in cascade with and following said first and second filters for clipping transients in said second signal.
Claim 16
Dependent Claim
80 words
A signal processing system according to claim 1 comprising switch means for selecting the compression or expansion operating mode of said system, said switch means selectively effecting signal connections whereby for compression mode said further signal path is responsive to said input signal and said combining means combines said first and second signals additively and whereby for expansion mode said further signal path is responsive to said output signal and said combining means combines said first and second signals subtractively.
Claim 17
Dependent Claim
73 words
A signal processing system according to claim 11 comprising switch means for selecting compression or expansion operating mode of said system; said main signal path including subtractive combining means followed by additive combining means; said further signal path being responsive to the output of said subtractive combining means; and said switch means coupling said second signal to said additive combining means for compression mode and to said subtractive combining means for expansion mode.
Claim 18
Dependent Claim
78 words
A signal processing system according to claim 1 comprising switch means for selecting the compression or expansion operating mode of said system, said switch means effecting signal connections whereby for compression mode said further signal path is responsive to said output signal and said coMbining means combines said first and second signals additively and whereby for expansion mode said further signal path is responsive to said input signal and said combining means combines first and second signals subtractively.
Claim 19
Dependent Claim
74 words
A signal processing system according to claim 1 comprising switch means for selecting the compression or expansion operating mode of said system; said main signal path including additive combining means followed by subtractive combining means; said further signal paths being responsive to the output of said additive combining means; and said switch means coupling said second signal to said additive combining means for compression mode and to said subtractive combining means for expansion mode.
Claim 20
Dependent Claim
41 words
A signal processing system according to claim 1 comprising switch means for disabling said further path, whereby the processing action of said system can be disabled and said system transfers said input signal to the output in a substantially proportional manner.
Claim 21
Dependent Claim
299 words
A signal processing system for producing an output signal in response to an input signal comprising a main signal path responsive to said input signal and including means for providing in a specified frequency band a first signal substantially proportional to said input signal; a further signal path coupled to said main signal path and responsive to a signal derived from said main signal path for producing a second signal in said specified frequency band, and signal combining means for combining said first and second signals to produce said output signal, said further signal path including a first filter having fixed-value components for providing high-pass characteristics with a cutoff frequency within said specified frequency band; and means for limiting the amplitude of the output signal of the further signal path; said means including a second filter connected in cascade with said first filter and having variable cutoff characteristics; said second filter including a variable impedance means responsive to an increase in the amplitude of at least one of the output of and the input to said further signal path for altering said cutoff characteristics from passing substantially all frequencies in said specified frequency band under low-level input signal conditions to progressively passing only the high frequencies therein, and providing a cutoff frequency which shifts upwards sufficiently to attenuate, in combination with the said high-pass characteristics of said first filter, any high-level input signal components at any given frequency in said specified frequency band to a specified level corresponding in said second signal to a small fractional part of the maximum level of said input signal, while permitting input signal components below said specified level at higher frequencies than said given frequency to pass through said filters and to appear in said second signal with a lesser degree of attenuation.
Claim 22
Dependent Claim
299 words
A signal processing system for producing an output signal in response to an input signal comprising a main signal path responsive to said input signal and including means for providing in a specified frequency band a first signal substantially proportional to said input signal; a further signal path coupled to said main signal path and responsive to a signal derived from said main signal path for producing a second signal in said specified frequency band, and signal combining means for combining said first and second signals to produce said output signal, said further signal path including a first filter having fixed-value components for providing high-pass characteristics with a cutoff frequency within said specified frequency band; and means for limiting the amplitude of the output signal of the further signal path; said means including a second filter connected in cascade with said first filter and having variable cutoff characteristics; said second filter including a variable impedance means responsive to an increase in the amplitude of at least one of the output of and the input to said further signal path for altering said cutoff characteristics from passing substantially all frequencies in said specified frequency band under low-level input signal conditions to progressively passing only the high frequencies therein, and providing a cutoff frequency which shifts upwards sufficiently to attenuate, in combination with the said high-pass characteristics of said first filter, any high-level input signal components at any given frequency in said specified frequency band to a specified level corresponding in said second signal to a small fractional part of the maximum level of said input signal, while permitting input signal components below said specified level at higher frequencies than said given frequency to pass through said filters and to appear in said second signal with a lesser degree of attenuation.
Claim 23
Dependent Claim
45 words
A signal processing system according to claim 26 comprising means responsive to the output of said further signal path to control the impedance of said variable impedance means as a function of frequency such that said small fractional part decreases as said given frequency increases.
Claim 24
Dependent Claim
43 words
A signal processing system according to claim 20 wherein said further signal path is responsive to said input signal; and wherein said signal combining means additively combines said first signal and said second signal, whereby said signal processing system operates as a compressor.
Claim 25
Dependent Claim
66 words
In a tape recorder, for approximately correcting the high-frequency emphasis introduced by a signal compressor in accordance with claim 22 to the signal as recorded on a tape being played back by said recorder, the improvement consisting in a passive equalization network for approximately correcting said emphasis, the network comprising a series resistance followed by a shunt arm which includes a resistor and capacitor in series.
Claim 26
Dependent Claim
43 words
A sigNal processing system according to claim 20 wherein said further signal path is responsive to said output signal; and wherein said signal combining means subtractively combines said second signal and said first signal, whereby said signal processing system operates as an expander.
Claim 27
Dependent Claim
74 words
A signal processing system according to claim 20 comprising switch means for selecting the compression or expansion operating mode of said system; said main signal path including subtractive combining means followed by additive combining means; said further signal path being responsive to the output of said subtractive combining means; and said switch means coupling said second signal to said additive combining means for compression mode and to said subtractive combining means for expansion mode.
Claim 28
Dependent Claim
41 words
A signal processing system according to claim 20 comprising switch means for disabling said further path, whereby the processing action of said system can be disabled and said system transfers said input signal to the output in a substantially proportional manner.
Claim 29
Independent Claim
146 words
A method of processing an input signal to modify the dynamic range thereof, wherein first and second signal components are derived in response to said input signal and combined to form an output signal; said first signal component being substantially proportional to said input signal within a frequency band extending between first and second limits; and said second signal component being subjected to the action of a first filter having a fixed cutoff frequency lying between said first and second limits and passing signals between said first limit and said cutoff frequency and the action of a second filter having a variable cutoff frequency which is shifted progressively away from said second limit as said second signal component tends to increase, thereby to limit said second signal component to a small fractional part of said first signal component when said input signal is at maximum level.
Claim 30
Independent Claim
146 words
A method of processing an input signal to modify the dynamic range thereof, wherein first and second signal components are derived in response to said input signal and combined to form an output signal; said first signal component being substantially proportional to said input signal within a frequency band extending between first and second limits; and said second signal component being subjected to the action of a first filter having a fixed cutoff frequency lying between said first and second limits and passing signals between said first limit and said cutoff frequency and the action of a second filter having a variable cutoff frequency which is shifted progressively away from said second limit as said second signal component tends to increase, thereby to limit said second signal component to a small fractional part of said first signal component when said input signal is at maximum level.
References Cited (Backward Citations)
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1974-12-27 | 1975-06-28 | 1975-12-28 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1978-12-27 | 1979-06-28 | 1979-12-28 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1982-12-27 | 1983-06-28 | 1983-12-28 | $7700.00 | Window Closed / Lapsed |