US3980964A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Noise reduction circuit
Assignee: Individual
•
Filing: 1975-06-20
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Granted: 1976-09-14
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Expires: 1995-06-20
Abstract
Abstract A noise reduction circuit for uncompressed and randomly compressed audio signals comprises a variable gain stage providing a gain which varies with the magnitude of a DC control signal fed to a control terminal thereby, an AC to DC converter for generating a DC signal proportional to the amplitude of the AC signal fed thereto and a filter for passing middle and upper frequencies and for eliminating or substantially reducing the low frequencies fed thereto and coupled between the audio signal input and the input to said AC to DC converter.
Inventors
- 👤 Robert M. Grodinsky
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-26 16:02
CPC Classifications
H; H03; H03G; H03G9/00; H03G9/02; H03G9/025
Claims Analysis
Total Claims: 19
Claim 1
Independent Claim
259 words
A noise reduction and expander circuit for uncompressed and randomly compressed audio signals encompassing the low, middle and upper frequency range, said circuit comprising: main audio signal input terminal means at which said audio signals are applied, audio signal level varying means forming part of an expander circuit and having input terminal means coupled to said main audio signal input terminal means, control terminal means and output terminal means, the signal level varying means providing an output signal level at said output terminal means which signal varies in response to the magnitude of a control signal fed to said control terminal means, said signal level varying means being substantially non-frequency selective over the useful audio range for all operative levels of the control signal fed thereof, and control means for generating and feeding a control signal to said control terminal means of said signal level varying means and including means including filter means coupled to a source of said audio signal encompassing said low, middle and upper frequencies for passing the higher audio signal frequencies above said low frequencies which higher frequencies contain appreciable energy content of the harmonics of the audio signal and for eliminating or substantially reducing the low frequencies fed thereto and effecting the coupling to said control terminal means of a control signal resulting from the signal passed by said filter means, which control signal expands the audio signal fed to the input terminal means of said signal level varying means in proportion to the amplitude of the resultant signal passed by said filter means.
Claim 2
Dependent Claim
259 words
A noise reduction and expander circuit for uncompressed and randomly compressed audio signals encompassing the low, middle and upper frequency range, said circuit comprising: main audio signal input terminal means at which said audio signals are applied, audio signal level varying means forming part of an expander circuit and having input terminal means coupled to said main audio signal input terminal means, control terminal means and output terminal means, the signal level varying means providing an output signal level at said output terminal means which signal varies in response to the magnitude of a control signal fed to said control terminal means, said signal level varying means being substantially non-frequency selective over the useful audio range for all operative levels of the control signal fed thereof, and control means for generating and feeding a control signal to said control terminal means of said signal level varying means and including means including filter means coupled to a source of said audio signal encompassing said low, middle and upper frequencies for passing the higher audio signal frequencies above said low frequencies which higher frequencies contain appreciable energy content of the harmonics of the audio signal and for eliminating or substantially reducing the low frequencies fed thereto and effecting the coupling to said control terminal means of a control signal resulting from the signal passed by said filter means, which control signal expands the audio signal fed to the input terminal means of said signal level varying means in proportion to the amplitude of the resultant signal passed by said filter means.
Claim 3
Dependent Claim
104 words
The noise reduction and expander circuit of claim 1 wherein said control means includes and AC to DC converter means having input terminal means and output terminal means, said AC to DC converter means generating at the latter output terminal means a DC signal proportional to the amplitude of the AC signal fed to the latter input terminal means thereof, said input terminal means of said AC to DC converter means being coupled to the output of said filter means, and means coupling the DC output of said AC to DC converter means to said control terminal means of said signal level varying means.
Claim 4
Dependent Claim
61 words
The noise reduction and expander circuit of claim 1 wherein said signal level varying means and said control means form a signal expanding system which for each 10db of dynamic range of the signal fed to said main audio signal input terminal means results in an expansion in dynamic range of the output signal of from about 2 to 6 db.
Claim 5
Dependent Claim
48 words
The noise reduction and expander circuit of claim 1 wherein said filter means is a band pass filter which substantially reduces frequencies below about 1 to 1.5 kilohertz and substantially reduces or eliminates from the output thereof frequencies above that containing appreciable harmonic energy of the audio signal.
Claim 6
Dependent Claim
56 words
The noise reduction and expander circuit of claim 2 wherein said AC to DC converter means includes rectifier means for rectifying the AC input thereof and ripple filter means of short time constant so the output of the AC to DC converter responds relatively quickly to the variations in dynamic range of the signal fed thereto.
Claim 7
Dependent Claim
59 words
The noise reduction and expander circuit of claim 2 wherein said AC to DC converter means includes a relatively fast acting short time constant filter circuit which provides a DC voltage output which follows the variation in dynamic range of the signals fed to the input terminal means of said converter but eliminates the cycle by cycle variations thereof.
Claim 8
Dependent Claim
45 words
The noise reduction and expander circuit of claim 6 wherein there is provided a relatively slow acting, longer time constant filter circuit responsive to the audio signal for coupling to the control terminal means of said signal level varying means a second DC control signal.
Claim 9
Dependent Claim
38 words
The noise reduction and expander circuit of claim 1 wherein there is coupled between said source of audio signals and said control terminal means of said signal level varying means a circuit which compresses the signal fed thereto.
Claim 10
Dependent Claim
20 words
The noise reduction and expander circuit of claim 1 combined with a source of uncompressed or randomly compressed audio signals.
Claim 11
Dependent Claim
26 words
The noise reduction and expander circuit of claim 1 wherein said filter means substantially reduces most of the signal frequencies below about 1 to 1.5 kilohertz.
Claim 12
Dependent Claim
36 words
The noise reduction and expander circuit of claim 10 wherein said filter means passes frequencies without significant amplitude reduction at and above about 1 to 1.5 kilohertz to a frequency of at least about 5-8 kilohertz.
Claim 13
Dependent Claim
145 words
The noise reduction and expander circuit of claim 2 wherein said AC to DC converter includes a relatively fast time constant DC voltage filter circuit which responds relatively quickly to an increase or decrease in dynamic level of the signals fed to the input terminal means of said converter but eliminates the cycle by cycle variations thereof, means coupling the output of said filter circuit to said control terminal means of said signal level varying means, and there is provided a relatively slow acting longer time constant filter circuit responsive to the output of said relatively fast time constant DC filter circuit by coupling to the control terminal means of said signal level varying means a second DC signal which responds relatively slowly to changes in the input thereto and adds its effect to the control of the output of said signal level varying means.
Claim 14
Dependent Claim
71 words
The noise reduction and expander circuit of claim 12 wherein there is provided between said fast acting short time constant filter circuit of said AC to DC converter and said relatively slow acting longer time constant filter circuit an emitter-follower type isolating circuit which has an output which follows the output of said fast acting short time constant filter circuit and feeds the input of said longer time constant filter circuit.
Claim 15
Dependent Claim
83 words
The noise reduction circuit of claim 7 wherein said longer time constant filter circuit is responsive to the output of said relatively fast acting short time constant filter circuit, and the outputs of the relatively fast acting short time constant filter circuit and the relatively slow acting longer time constant filter circuit are each independent in controlling the output of said signal level varying means whose resultant output is the sum of the effects of each of the outputs of said filter circuits.
Claim 16
Dependent Claim
42 words
The noise reduction and expander circuit of claim 2 where the dynamic range of said control signal is approximately matched to the dynamic range of the input signal so as to act only over a predetermined range of input signal change level.
Claim 17
Dependent Claim
34 words
The noise reduction and expander circuit of claim 3 where the dynamic range of the control signal is limited to about 25db and the resulting total expansion is from about 5 to 15 db.
Claim 18
Dependent Claim
108 words
The noise reduction and expander circuit of claim 2 wherein there is associated with said AC to DC converter means relatively fast and relatively slow time constant DC voltage producing filter circuit means which respectively respond relatively quickly and slowly to an increase or decrease in dynamic level of the signals fed to the input terminal means of said converter means, and coupling means for coupling the outputs of said filter circuit means to said control terminal means of said signal level varying means so the outputs thereof to a substantial degree have their individual effects upon the control of the output of said signal level varying means.
Claim 19
Dependent Claim
125 words
The noise reduction and expander circuit of claim 2 wherein there is associated with said AC to DC converter means two DC output producing filter circuits responsive to the change in dynamic range of the AC signal input to the AC to DC converter means, one of said filter circuits having fast charging and discharging capacitor charge and discharge circuits and the other of said filter circuits having relatively slow charging and discharging capacitor charge and discharge circuits, and coupling means for coupling the DC outputs of said filter circuits to said control terminal means of said signal level varying means so the outputs thereof to a substantial degree have their individual effects upon the control of the output of said signal level varying means.
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) | 1979-09-14 | 1980-03-15 | 1980-09-14 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1983-09-14 | 1984-03-15 | 1984-09-14 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1987-09-14 | 1988-03-15 | 1988-09-14 | $7700.00 | Window Closed / Lapsed |