US3857104A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Noise filter
Assignee: Individual
•
Filing: 1973-10-01
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Granted: 1974-12-24
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Expires: 1993-10-01
Abstract
Abstract A composite signal having a desired signal content and a noisy signal content is fed to a plurality of contiguous narrow band nonlinear filters connected in parallel. Each filter has a controllable discrimination threshold and together cover the audio spectrum where noise signals are considered objectionable. A noise tracker connected to the same signal source detects the noise level whenever the desired signal is either absent or substantially reduced. The discrimination threshold of each of the narrow band filters is controlled by the output of the noise tracker, which thereby controls the ability of each of the narrow band filters to pass a signal as a function of the noise signal being detected. The outputs of each of the narrow band filters are connected together and fed to a combining circuit where the spectral power in the output of all of said filters is combined in the power phase relationship. The gain of the individual narrow band filters is reduced in the presence of noise. In the presence of a strong desired signal the gain is not attenuated and in this manner the signal to noise ratio of the signal is improved.
Inventors
- 👤 J Sacks
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-25 21:56
CPC Classifications
H; H03; H03G; H03G9/00; H03G9/02; H03H; H03H11/00; H03H11/02; H03H11/04; H03H11/0405
Claims Analysis
Total Claims: 17
Claim 1
Independent Claim
86 words
A noise filter comprising, an input narrow band filter adapted to be connected to a wide band source of audio frequencies, an amplitude controllable threshold nonlinear device that is fed by said input narrow band filter, and an output narrow band filter connected to the output of the nonlinear device having a band pass characteristic similar to the input filter, and a noise tracker connected to said non-linear device for generating a signal proportioned to noise whereby the amplitude threshhold of said non-linear device is controlled.
Claim 2
Dependent Claim
86 words
A noise filter comprising, an input narrow band filter adapted to be connected to a wide band source of audio frequencies, an amplitude controllable threshold nonlinear device that is fed by said input narrow band filter, and an output narrow band filter connected to the output of the nonlinear device having a band pass characteristic similar to the input filter, and a noise tracker connected to said non-linear device for generating a signal proportioned to noise whereby the amplitude threshhold of said non-linear device is controlled.
Claim 3
Dependent Claim
32 words
A filter according to claim 1 in which said nonlinear device comprises a bridge circuit having a changeable bias for controlling the amplitude threshold at which said circuit passes an input signal.
Claim 4
Dependent Claim
143 words
A noise tracker comprising, a first high pass filter adapted to pass signal and noise frequencies, a first channel having an input connected to the output of said high pass filter and an output for detecting the presence of a desired signal as a function of the zero crossings of the incoming signal, a rectifier circuit connected to the output of said high pass filter and feeding a gate circuit controlled by the output of said first channel, and a smaple and hold circuit responsive to the output of said gate when continuously sampling and generating a signal having an amplitude that bears a direct relationship to the amplitude of incoming noise frequencies, said sample and hold circuit having a substantially long time constant for holding the last sample in the presence of a desired output from the first channel opening the gate.
Claim 5
Dependent Claim
143 words
A noise tracker comprising, a first high pass filter adapted to pass signal and noise frequencies, a first channel having an input connected to the output of said high pass filter and an output for detecting the presence of a desired signal as a function of the zero crossings of the incoming signal, a rectifier circuit connected to the output of said high pass filter and feeding a gate circuit controlled by the output of said first channel, and a smaple and hold circuit responsive to the output of said gate when continuously sampling and generating a signal having an amplitude that bears a direct relationship to the amplitude of incoming noise frequencies, said sample and hold circuit having a substantially long time constant for holding the last sample in the presence of a desired output from the first channel opening the gate.
Claim 6
Dependent Claim
20 words
A noise tracker according to claim 3 in which said first high-pass filter passes substantially all frequencies above 1,000 cycles.
Claim 7
Dependent Claim
75 words
A noise tracker according to claim 3 in which said first signal comprises a zero crossing detector for generating a pulse at every crossing, means for differentiating and full wave rectifying said pulses, means for integrating and filtering said rectified pulses whereby a DC output signal is produced having an amplitude that varies as a function of the zero crossings of the incoming signal, and means for opening said gate with said DC output signal.
Claim 8
Dependent Claim
45 words
A noise tracker according to claim 3 which includes a second channel for generating an output signal as a function of amplitude change in the incoming signal, and in which either the output signal from said second channel or said first channel controls said gate.
Claim 9
Dependent Claim
116 words
A noise tracker according to claim 6 in which said second channel comprises a second high-pass filter having a low cutoff frequency that is higher than said first high-pass filter for passing the composite input signal, means for rectifying the composite input signal and feeding said rectified signal to an amplitude comparator and a low-pass filter, said low-pass filter having a substantially long time constant for generating a DC signal representative of the desired signal, the amplitude comparator continuously comparing the average signals from said low-pass filter and the rectified signals from the rectifier for generating an output signal in the presence of a change in amplitude of said rectified signal relative to said average signal.
Claim 10
Dependent Claim
19 words
A noise tracker, according to claim 6, in which said second channel passes substantially all frequencies over 5,000 cycles.
Claim 11
Dependent Claim
34 words
A noise tracker, according to claim 7, in which the output of said low-pass filter is fed to a scaling network for amplifying the instantaneous changes in the DC signal fed to the comparator.
Claim 12
Dependent Claim
142 words
A noise tracker comprising a first high-pass filter adapted to pass signal and noise frequencies substantially above a selected minimum, a first channel connected to the output of said high-pass filter for detecting the presence of a desired signal as a function of the zero crossings of the incoming signal, a rectifying circuit connected to the output of said high-pass filter and feeding a gate circuit controlled by the output of said first channel, and a sample and hold circuit responsive to the output of said normally closed gate for continuously sampling and generating a signal having an amplitude that bears a direct relationship to the amplitude of the incoming noise signal, said sample and hold circuit having a substantially long time constant for holding the last sample in the presence of a signal output from the first channel opening the gate.
Claim 13
Dependent Claim
142 words
A noise tracker comprising a first high-pass filter adapted to pass signal and noise frequencies substantially above a selected minimum, a first channel connected to the output of said high-pass filter for detecting the presence of a desired signal as a function of the zero crossings of the incoming signal, a rectifying circuit connected to the output of said high-pass filter and feeding a gate circuit controlled by the output of said first channel, and a sample and hold circuit responsive to the output of said normally closed gate for continuously sampling and generating a signal having an amplitude that bears a direct relationship to the amplitude of the incoming noise signal, said sample and hold circuit having a substantially long time constant for holding the last sample in the presence of a signal output from the first channel opening the gate.
Claim 14
Dependent Claim
150 words
A system according to claim 10 in which said noise tracker comprises a first high-pass filter adapted to pass signal and noise frequencies substantially above a selected minimum, a first channel connected to the output of said high-pass filter for detecting the presence of a desired signal as a function of the zero crossings of the incoming signal, a rectifying circuit connected to the output of said high-pass filter and feeding a gate circuit controlled by the output of said first channel and a sample and hold circuit responsive to the output of said normally closed gate for continuously sampling and generating a signal having an amplitude that bears a direct relationship to the amplitude of the incoming noise signal, said sample and hold circuit having a substantially long time constant for holding the last sample in the presence of a signal output from the first channel opening the gate.
Claim 15
Dependent Claim
159 words
In combination, a noise tracker connected to a signal source of generating a control signal proportional to the reciprocal of the noise, a plurality of narrow band channels, each comprising a narrow band filter for passing a desired spectral band of frequencies, a first linear multiplier having a first input from said narrow band filter and a second input from said noise tracker whereby the linear gain of the multiplier is a function of the reciprocal of the detected noise, a rectifier and shaper circuit connected to the output of said first linear multiplier for generating a DC signal that varies as a function of the amplitude of the spectral band of frequencies passed by the narrow band filter, and a second linear multiplier having a first input from said rectifier and shaper circuit and a second input from said narrow band filter whereby the DC signal from the rectifier and shaper circuit varies the gain of the multiplier.
Claim 16
Dependent Claim
159 words
In combination, a noise tracker connected to a signal source of generating a control signal proportional to the reciprocal of the noise, a plurality of narrow band channels, each comprising a narrow band filter for passing a desired spectral band of frequencies, a first linear multiplier having a first input from said narrow band filter and a second input from said noise tracker whereby the linear gain of the multiplier is a function of the reciprocal of the detected noise, a rectifier and shaper circuit connected to the output of said first linear multiplier for generating a DC signal that varies as a function of the amplitude of the spectral band of frequencies passed by the narrow band filter, and a second linear multiplier having a first input from said rectifier and shaper circuit and a second input from said narrow band filter whereby the DC signal from the rectifier and shaper circuit varies the gain of the multiplier.
Claim 17
Dependent Claim
24 words
A combination according to claim 12 in which each narrow band channel contains a weighting network responsive to known variations in the noise spectrum.
References Cited (Backward Citations)
No citation records indexed.
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1977-12-23 | 1978-06-24 | 1978-12-24 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1981-12-23 | 1982-06-24 | 1982-12-24 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1985-12-23 | 1986-06-24 | 1986-12-24 | $7700.00 | Window Closed / Lapsed |