Automatic gain selector for a noise suppression system
First Claim
1. An improved noise suppression system for attenuating the background noise from a noisy input signal to produce a noise-suppressed output signal, said noise suppression system comprising:
- means for separating the input signal into a plurality of pre-processed signals representative of selected frequency channels;
means for modifying an operating parameter of each of said plurality of pre-processed signals provided by said signal separating means to provide a plurality of post-processed signals; and
means responsive to said plurality of pre-processed signals for generating a modification signal having a selected modification value for each channel for application to said modifying means to enable the operating parameter to be modified, said modification signal generated by automatically selecting a modification value for each channel from one of a plurality of sets of modification values for that channel.
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Abstract
An automatic gain selector is disclosed for use with a noise suppression system which performs speech quality enhancement upon a noisy speech signal available at the input to generate a noise-suppressed speech signal at the output by spectral gain modification. The channel gain controller (240) of the present invention produces a modification signal (245), comprised of individual channel gain values, for application to a channel gain modifier (250). A particular gain table set is automatically selected from one of a plurality of gain tables (450) by a selector switch (470) and a noise level quantizer (440) in response to a multi-channel noise parameter, such as the overall average background noise level of the input signal. Then the individual channel gain values (455) are obtained from the particular gain table set in response to the individual channel signal-to-noise ratio estimate (235). Hence, each individual channel gain value is selected as a function of (a) the channel number, (b) the current channel SNR estimate, and (c) the overall average background noise level. The automatic gain selector further includes a gain smoothing filter (460) for smoothing these noise suppression gain factors on a per-sample basis thereby improving noise flutter performance caused by step discontinuities in frame-to-frame gain changes.
335 Citations
42 Claims
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1. An improved noise suppression system for attenuating the background noise from a noisy input signal to produce a noise-suppressed output signal, said noise suppression system comprising:
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means for separating the input signal into a plurality of pre-processed signals representative of selected frequency channels; means for modifying an operating parameter of each of said plurality of pre-processed signals provided by said signal separating means to provide a plurality of post-processed signals; and means responsive to said plurality of pre-processed signals for generating a modification signal having a selected modification value for each channel for application to said modifying means to enable the operating parameter to be modified, said modification signal generated by automatically selecting a modification value for each channel from one of a plurality of sets of modification values for that channel. - View Dependent Claims (4, 5, 6, 7)
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2. An improved noise suppression system for attenuating the background noise from a noisy input signal to produce a noise-suppressed output signal, said noise suppression system comprising:
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means for separating the input signal into a plurality of pre-processed signals representative of selected frequency channels, each of said plurality of pre-processed signals comprised of a plurality of frames, each frame comprised of a plurality of samples of said input signal; means for modifying an operating parameter of each of said plurality of pre-processed signals provided by said signal separating means to provide a plurality of post-processed signals; and means responsive to said plurality of pre-processed signals for generating a modification signal for application to said modifying means to enable the operating parameter to be modified, said modification signal generating means including means for smoothing said modification signal multiple times per frame. - View Dependent Claims (3)
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8. An improved noise suppression system for attenuating the background noise from a noisy input signal to produce a noise-suppressed output signal, said noise suppression system comprising:
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means for separating the input signal into a plurality of pre-processed signals representative of selected frequency channels; means for generating an estimate of the signal-to-noise ratio (SNR) in each individual channel; means for producing a gain value for each channel by automatically selecting one of a plurality of gain tables in response to a multi-channel noise parameter, and selecting one of a plurality of gain values from the selected gain table in response to said channel SNR estimates and the channel number; and means for modifying the gain of each of said plurality of pre-processed signals provided by said signal separating means in response to said gain values to provide a plurality of post-processed signals. - View Dependent Claims (10, 11, 12, 13, 14, 15)
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9. An improved noise suppression system for attenuating the background noise from a noisy input signal to produce a noise-suppressed output signal, said noise suppression system comprising:
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means for separating the input signal into a plurality of pre-processed signals representative of selected frequency channels, each of said plurality of pre-processed signals comprised of a plurality of frames, each frame comprised of a plurality of samples of said input signal; means for generating an estimate of the signal-to-noise ratio (SNR) in each individual channel once each frame; means for producing a raw gain value for each channel in response to said SNR estimates once each frame; means for smoothing said raw gain values multiple times per frame; and means for modifying the gain of each of said plurality of pre-processed signals provided by said signal separating means in response to said smoothed gain values to provide a plurality of post-processed signals. - View Dependent Claims (16)
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17. An improved noise suppression system for attenuating the background noise from a noisy pre-processed input signal to produce a noise-suppressed post-processed output signal by spectral gain modification, said noise suppression system comprising:
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signal dividing means for separating the pre-processed input signal into a plurality of selected frequency bands, thereby producing a plurality of pre-processed channels; channel energy estimation means for generating an estimate of the energy in each of said plurality of pre-processed channels; channel noise estimation means for generating an estimate of the signal-to-noise ratio (SNR) of each individual channel based upon said channel energy estimates and an estimate of the current background noise energy for that individual channel; channel gain controlling means for providing channel gain values, said channel gain controlling means having a plurality of gain tables, each gain table having predetermined individual channel gain values corresponding to various individual channel SNR estimates, said channel gain controlling means further having gain table selection means for automatically selecting one of said plurality of gain tables according to the overall average background noise level of said input signal; channel gain modifying means for adjusting the gain of each of said plurality of pre-processed channels provided by said signal dividing means according to said channel gain values, thereby producing a plurality of post-processed channels; and channel combination means for recombining said plurality of post-processed channels to produce said post-processed output signal. - View Dependent Claims (18, 19, 20, 21, 22, 23, 24)
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25. An improved channel gain controller for use with a spectral gain modification noise suppression system having separating means to divide a noisy input signal into a plurality of channels, and a modifying means to adjust the gain of said channels according to gain values provided by the channel gain controller to produce a plurality of noise-suppressed output channels, said channel gain controller comprising:
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a plurality of gain tables, each having predetermined individual channel gain values corresponding to various individual channel signal-to-noise ratio (SNR) estimates; and gain table selection means for automatically selecting one of said plurality of gain tables according to the overall average background noise level of said noisy input signal. - View Dependent Claims (26, 27, 28, 29, 30)
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31. The method of attenuating the background noise from a noisy input signal to produce a noise-suppressed output signal comprising the steps of:
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separating the input signal into a plurality of pre-processed signals representative of selected frequency channels; modifying an operating parameter of each of said plurality of pre-processed signals to provide a plurality of post-processed signals; and generating a modification signal responsive to said plurality of pre-processed signals, said modification signal having a selected modification value for each channel to enable the operating parameter to be modified, said modification signal generated by automatically selecting a modification value for each channel from one of a plurality of sets of modification values for that channel. - View Dependent Claims (34, 35)
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32. The method of attenuating the background noise from a noisy input signal to produce a noise-suppressed output signal in a noise suppression system comprising the steps of:
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separating the input signal into a plurality of pre-processed signals representative of selected frequency channels, each of said plurality of pre-processed signals comprised of a plurality of frames, each frame comprised of a plurality of samples of said input signal; modifying an operating parameter of each of said plurality of pre-processed signals to provide a plurality of post-processed signals; and generating a modification signal responsive to said plurality of pre-processed signals, said modification signal having a selected modification value for each channel to enable the operating parameter to be modified, said modification values being smoothed multiple times per frame to reduce discontinuities in said modification signal. - View Dependent Claims (33)
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36. The method of attenuating the background noise from a noisy input signal to produce a noise-suppressed output signal by spectral gain modification, comprising the steps of:
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separating the input signal into a plurality of pre-processed signals representative of selected frequency channels; generating an estimate of the signal-to-noise ratio (SNR) in each individual channel; producing a gain value for each channel by automatically selecting one of a plurality of gain tables in response to a multi-channel noise parameter, and selecting one of a plurality of gain values from the selected gain table in response to said channel SNR estimates and the channel number; and modifying the gain of each of said plurality of pre-processed signals in response to said gain values to provide a plurality of post-processed signals. - View Dependent Claims (38, 40, 41, 42)
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37. The method of attenuating the background noise from a noisy input signal to produce a noise-suppressed output signal by spectral gain modification, comprising the steps of:
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separating the input signal into a plurality of pre-processed signals representative of selected frequency channels, each of said plurality of pre-processed signals comprised of a plurality of frames, each frame comprised of a plurality of samples of said input signal; generating an estimate of the signal-to-noise ratio (SNR) in each individual channel once each frame; producing a raw gain value for each channel in response to said SNR estimates once each frame; smoothing said raw gain values multiple times per frame; and modifying the gain of each of said plurality of pre-processed signals in response to said smoothed gain values to provide a plurality of post-processed signals. - View Dependent Claims (39)
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Specification