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US4630304A
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Automatic background noise estimator for a noise suppression system
Assignee: Motorola Solutions Inc
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Filing: 1985-07-01
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Granted: 1986-12-16
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Expires: 2005-07-01
Abstract
Abstract An improved background noise estimator (320) is disclosed for use with a noise suppression system (300) for generating an estimate of the background noise power spectral density provided to noise suppressor (310), which performs speech quality enhancement upon the pre-processed speech-plus-noise signal available at the input to generate a clean post-processed speech signal at the output. Background noise estimator (320) utilizes an energy valley detector based upon post-processed speech to perform the speech/noise classification, and a noise spectral estimator based upon pre-processed speech to generate an estimate of the background noise power spectral density. As a result, the background noise estimate supplied to the noise suppressor is a more accurate measurement of the background noise energy, since it is performed during a more accurate determination of the occurrences of pauses in the speech.
Inventors
- 👤 David E. Borth
- 👤 Ira A. Gerson
- 👤 Richard J. Vilmur
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-24 21:10
CPC Classifications
G; G10; G10L; G10L21/00; G10L21/02; G10L21/0208; G10K; G10K2210/00; G10K2210/10; G10K2210/108; G10K2210/30; G10K2210/301; G10K2210/3011; G10K2210/3012; G10K2210/3023; H; H04; H04R; H04R2225/00; H04R2225/43; H04R25/00; H04R25/50; H04R25/505
Claims Analysis
Total Claims: 37
Claim 1
Independent Claim
97 words
An improved background noise estimator adapted for use with a noise suppression system wherein the background noise from a noisy pre-processed input signal is attenuated by spectral gain modification to produce a noise-suppressed post-processed output signal, said background noise estimator comprising: noise estimation means for generating and storing an estimate of the background noise power spectral density of the pre-processed signal; and noise detection means for periodically detecting the minima of the post-processed signal energy, and for controlling said noise estimation means in response thereto such that said background noise estimate is updated only during said minima.
Claim 2
Dependent Claim
97 words
An improved background noise estimator adapted for use with a noise suppression system wherein the background noise from a noisy pre-processed input signal is attenuated by spectral gain modification to produce a noise-suppressed post-processed output signal, said background noise estimator comprising: noise estimation means for generating and storing an estimate of the background noise power spectral density of the pre-processed signal; and noise detection means for periodically detecting the minima of the post-processed signal energy, and for controlling said noise estimation means in response thereto such that said background noise estimate is updated only during said minima.
Claim 3
Dependent Claim
73 words
The background noise estimator according to claim 1, wherein said noise estimation means includes: channel energy estimation means for generating an estimate of the pre-processed signal energy in each of a plurality of selected frequency bands; and storage means for storing each of said energy estimates as a per-channel noise estimate, and for continuously providing an estimate of the background noise power spectral density of the pre-processed signal to said noise suppression system.
Claim 4
Dependent Claim
38 words
The background noise estimator according to claim 2, wherein said channel energy estimation means includes: means for separating said pre-processed signal into a plurality of frequency channels; and means for detecting the energy in each of said channels.
Claim 5
Dependent Claim
23 words
The background noise estimator according to claim 3, wherein said separating means includes a plurality of bandpass filters covering the voice frequency range.
Claim 6
Dependent Claim
37 words
The background noise estimator according to claim 4, wherein said plurality of bandpass filters is further comprised of a bank of approximately 14 contiguous bandpass filters covering the frequency range from approximately 250 Hz. to 3400 Hz.
Claim 7
Dependent Claim
30 words
The background noise estimator according to claim 3, wherein said detecting means includes a plurality of full-wave rectifiers coupled to low-pass filters, thereby providing an energy estimate for each channel.
Claim 8
Dependent Claim
51 words
The background noise estimator according to claim 2, wherein said storage means includes: smoothing means for providing a time-averaged value of each of said energy estimates generated by said channel energy estimation means; and memory means for storing each of said time-averaged values from said smoothing means as per-channel noise estimates.
Claim 9
Dependent Claim
32 words
The background noise estimator according to claim 7, wherein said memory means is preset upon system initialization with initialization values which represent per-channel noise estimates approximating that of a clean input signal.
Claim 10
Dependent Claim
104 words
The background noise estimator according to claim 1, wherein said noise detection means includes: channel energy estimation means for generating an estimate of the post-processed signal energy in each of a plurality of selected frequency bands; channel combination means for combining the plurality of said energy estimates into a single overall energy estimate; valley detection means for periodically detecting the minima of said overall energy estimate, thereby generating a valley detect signal; and signal controlling means coupled to said noise estimation means and controlled by said valley detect signal for providing new background noise estimates to said noise estimation means only during said minima.
Claim 11
Dependent Claim
38 words
The background noise estimator according to claim 9, wherein said channel energy estimation means includes: means for separating said post-processed signal into a plurality of frequency channels; and means for detecting the energy in each of said channels.
Claim 12
Dependent Claim
23 words
The background noise estimator according to claim 10, wherein said separating means includes a plurality of bandpass filters covering the voice frequency range.
Claim 13
Dependent Claim
37 words
The background noise estimator according to claim 11, wherein said plurality of bandpass filters is further comprised of a bank of approximately 14 contiguous bandpass filters covering the frequency range from approximately 250 Hz. to 3400 Hz.
Claim 14
Dependent Claim
30 words
The background noise estimator according to claim 10, wherein said detecting means includes a plurality of full-wave rectifiers coupled to low-pass filters, thereby providing an energy estimate for each channel.
Claim 15
Dependent Claim
30 words
The background noise estimator according to claim 9, wherein said channel combination means includes means for summing the plurality of detected energy estimates to provide a single overall energy estimate.
Claim 16
Dependent Claim
106 words
The background noise estimator according to claim 9, wherein said valley detection means includes: means for storing the numerical value of the previous detected minima as a previous valley level; means for comparing the present numerical value of the overall energy estimate to said previous valley level; means for increasing said previous valley level at a slow rate when said present numerical value is greater than said previous valley level; and means for decreasing said previous valley level at a rapid rate when said present numerical value is less than said previous valley level, thereby updating said previous valley level to provide a current valley level.
Claim 17
Dependent Claim
26 words
The background noise estimator according to claim 15, wherein said rapid rate for updating said previous valley level exhibits a time constant of approximately 40 milliseconds.
Claim 18
Dependent Claim
26 words
The background noise estimator according to claim 15, wherein said slow rate for updating said previous valley level exhibits a time constant of approximately 1000 milliseconds.
Claim 19
Dependent Claim
66 words
The background noise estimator according to claim 15, wherein said valley detection means further includes: means for adding a selected valley offset to said current valley level, thereby providing a noise threshold level; and means for comparing said present numerical value to said noise threshold level, thereby generating a positive valley detect signal only when said present numerical value is less than said noise threshold level.
Claim 20
Dependent Claim
23 words
The background noise estimator according to claim 18, wherein said selected valley offset is approximately 6 dB relative to said current valley level.
Claim 21
Dependent Claim
23 words
The background noise estimator according to claim 18, wherein said present numerical value and said previous valley level are expressed in logarithmic terms.
Claim 22
Dependent Claim
49 words
The background noise estimator according to claim 9, wherein said signal controlling means includes: channel switch means coupled to said noise estimation means and controlled by said valley detect signal for providing new background noise estimates to said noise estimation means only when said valley detect signal is positive.
Claim 23
Dependent Claim
155 words
An improved background noise estimator adapted for use with a noise suppression system wherein the background noise from a noisy pre-processed input signal is attenuated by spectral gain modification to produce a noise-suppressed post-processed output signal, said background noise estimator comprising: storage means for storing an estimate of the background noise energy of the pre-processed signal in each of a plurality of selected frequency bands as per-channel noise estimates, and for continuously providing an estimate of the background noise power spectral density of the pre-processed signal to said noise suppression system; valley detection means for periodically detecting the minima of an overall estimate of the energy of said post-processed signal in each of a plurality of selected frequency bands, thereby generating a valley detect signal; and signal controlling means coupled to said storage means and controlled by said valley detect signal for providing new background noise estimates to said storage means only during said minima.
Claim 24
Dependent Claim
155 words
An improved background noise estimator adapted for use with a noise suppression system wherein the background noise from a noisy pre-processed input signal is attenuated by spectral gain modification to produce a noise-suppressed post-processed output signal, said background noise estimator comprising: storage means for storing an estimate of the background noise energy of the pre-processed signal in each of a plurality of selected frequency bands as per-channel noise estimates, and for continuously providing an estimate of the background noise power spectral density of the pre-processed signal to said noise suppression system; valley detection means for periodically detecting the minima of an overall estimate of the energy of said post-processed signal in each of a plurality of selected frequency bands, thereby generating a valley detect signal; and signal controlling means coupled to said storage means and controlled by said valley detect signal for providing new background noise estimates to said storage means only during said minima.
Claim 25
Dependent Claim
55 words
The background noise estimator according to claim 22, wherein said storage means includes: smoothing means for providing a time-averaged value of each of said background noise energy estimates of the pre-processed signal in a particular frequency band; and memory means for storing each of said time-averaged values from said smoothing means as per-channel noise estimates.
Claim 26
Dependent Claim
32 words
The background noise estimator according to claim 23, wherein said memory means is preset upon system initialization with initialization values which represent per-channel noise estimates approximating that of a clean input signal.
Claim 27
Dependent Claim
106 words
The background noise estimator according to claim 22, wherein said valley detection means includes: means for storing the numerical value of the previous detected minima as a previous valley level; means for comparing the present numerical value of the overall energy estimate to said previous valley level; means for increasing said previous valley level at a slow rate when said present numerical value is greater than said previous valley level; and means for decreasing said previous valley level at a rapid rate when said present numerical value is less than said previous valley level, thereby updating said previous valley level to provide a current valley level.
Claim 28
Dependent Claim
26 words
The background noise estimator according to claim 25, wherein said rapid rate for updating said previous valley level exhibits a time constant of approximately 40 milliseconds.
Claim 29
Dependent Claim
26 words
The background noise estimator according to claim 25, wherein said slow rate for updating said previous valley level exhibits a time constant of approximately 1000 milliseconds.
Claim 30
Dependent Claim
66 words
The background noise estimator according to claim 25, wherein said valley detection means further includes: means for adding a selected valley offset to said current valley level, thereby providing a noise threshold level; and means for comparing said present numerical value to said noise threshold level, thereby generating a positive valley detect signal only when said present numerical value is less than said noise threshold level.
Claim 31
Dependent Claim
23 words
The background noise estimator according to claim 28, wherein said selected valley offset is approximately 6 dB relative to said current valley level.
Claim 32
Dependent Claim
47 words
The background noise estimator according to claim 22, wherein said signal controlling means includes: channel switch means coupled to said storage means and controlled by said valley detect signal for providing new background noise estimates to said storage means only when said valley detect signal is positive.
Claim 33
Dependent Claim
23 words
The background noise estimator according to claim 28, wherein said present numerical value and said previous valley level are expressed in logarithmic terms.
Claim 34
Independent Claim
84 words
The method of estimating background noise in a noise suppression system, wherein the background noise from a noisy pre-processed input signal is attenuated by spectral gain modification to produce a noise-suppressed post-processed output signal, comprising the steps of: periodically detecting the minima of the post-processed signal energy; providing a noise detection signal only when said minima is detected; and generating and storing an estimate of the background noise power spectral density of the pre-processed signal only during the presence of said noise detection signal.
Claim 35
Independent Claim
84 words
The method of estimating background noise in a noise suppression system, wherein the background noise from a noisy pre-processed input signal is attenuated by spectral gain modification to produce a noise-suppressed post-processed output signal, comprising the steps of: periodically detecting the minima of the post-processed signal energy; providing a noise detection signal only when said minima is detected; and generating and storing an estimate of the background noise power spectral density of the pre-processed signal only during the presence of said noise detection signal.
Claim 36
Independent Claim
104 words
The method of estimating background noise in a noise suppression system, wherein the background noise from a noisy pre-processed input signal is attenuated by spectral gain modification to produce a noise-suppressed post-processed output signal, comprising the steps of: periodically detecting the minima of an overall estimate of the energy of the post-processed signal in each of a plurality of selected frequency bands; providing a positive valley detect signal only when said minima is detected; and storing an estimate of the energy of the pre-processed signal in each of a plurality of selected frequency bands only during the presence of said positive valley detect signal.
Claim 37
Independent Claim
104 words
The method of estimating background noise in a noise suppression system, wherein the background noise from a noisy pre-processed input signal is attenuated by spectral gain modification to produce a noise-suppressed post-processed output signal, comprising the steps of: periodically detecting the minima of an overall estimate of the energy of the post-processed signal in each of a plurality of selected frequency bands; providing a positive valley detect signal only when said minima is detected; and storing an estimate of the energy of the pre-processed signal in each of a plurality of selected frequency bands only during the presence of said positive valley detect signal.
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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) | 1989-12-15 | 1990-06-16 | 1990-12-16 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1993-12-15 | 1994-06-16 | 1994-12-16 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1997-12-15 | 1998-06-16 | 1998-12-16 | $7700.00 | Window Closed / Lapsed |