Noise suppression

• US 7,283,956 B2
• Filed: 09/18/2002
• Issued: 10/16/2007
• Est. Priority Date: 09/18/2002
• Status: Active Grant

• Current Assignee: Google Technology Holdings LLC (Alphabet Inc.)
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Ashley, James Patrick, McLaughlin, Michael Joseph, Ramabadran, Tenkasi Vaideeswaran
• Primary Examiner(s): Hudspeth; David
• Assistant Examiner(s): Ng; Eunice
• Application Number:
  US10/245,963
• Publication Number:
  US 20040052384A1
• Time in Patent Office: 1,854 Days
• Field of Search: None
• US Class Current: 704/228
• CPC Class Codes: H04B 1/1027 assessing signal quality or detecting noise/interference for the received signal

Abstract

A method and apparatus for noise suppression is described herein. The channel gain is controlled based on a degree of variability of the background noise. The noise variability estimate is used in conjunction with a variable attenuation concept to produce a family of gain curves that are adaptively suited for a variety of combinations of long-term peak SNR and noise variability. More specifically, a measure of the variability of the background noise is used to provide an optimized threshold that reduces the occurrence of non-stationary background noise entering into the transition region of the gain curve.

Claims

1. An apparatus comprising:

a noise variability estimator determining an amount of variability of background noise (σ

_n) in a speech-plus-noise signal and for determining an SNR gain threshold (σ

_th); and

a channel gain generator adjusting a gain (γ

_DB) applied to the speech-plus-noise signal based on the SNR gain threshold such that

γ

_DB(i)=μ

_g(σ

_q″

(i)−

σ

_th(σ

_n))+γ

_n

wherein

μ

_g is a gain slope,

σ

_q″

(i) is a channel SNR for channel i,

γ

_n is a minimum overall gain.

2. The apparatus of claim 1 wherein the speech-plus-noise signal is attenuated a first amount when the variability in background noise is high, otherwise the speech-plus-noise signal is attenuated a second amount.

3. The apparatus of claim 1 wherein the channel gain generator adjusts the gain of the speech-plus-noise signal by increasing the signal-to-noise (SNR) gain threshold when there exists a high variability in the background noise, wherein the speech-plus-noise signal will have a maximum attenuation when the SNR value of the speech-plus-noise signal is below the SNR gain threshold.

4. The apparatus of claim 3 wherein the maximum attenuation is based on the variability in background noise.

5. The apparatus of claim 1 farther comprising:

a channel signal-to-noise (SNR) estimator; and

wherein the noise variability estimator comprises an SNR variability estimator.

6. An apparatus for noise suppression, the apparatus comprising:

a channel signal energy estimator for estimating a total energy of a speech-plus-noise signal;

a noise energy estimator for estimating a noise energy of the speech-plus-noise signal;

a channel signal-to-noise (SNR) estimator having the noise energy estimate and the total energy estimate as an input and outputting an SNR estimate of the speech-plus-noise signal;

a SNR variability estimator for estimating the SNR variability (σ

_n) of the noise energy estimate and for determining an SNR gain threshold (σ

_th); and

a channel gain generator for adjusting a gain (γ

_DB) of the speech-plus-noise signal based on the SNR variability of the noise energy estimate such that

γ

_DB(i)=μ

_g(σ

_q″

(i)−

σ

_th(σ

_n))+γ

_n

wherein

μ

_g is a gain slope,

σ

_q″

(i) is a channel SNR for channel i,

γ

_n is a minimum overall gain.

7. The apparatus of claim 6 wherein the speech-plus-noise signal is attenuated a first amount when the SNR variability is high, otherwise the speech-plus-noise signal is attenuated a second amount.

8. The apparatus of claim 6 wherein the channel gain generator increases an SNR threshold when there exists a high SNR variability, wherein the speech-plus-noise signal will have a maximum attenuation when the SNR estimate of the speech-plus-noise signal is below the SNR threshold.

9. The apparatus of claim 8 wherein the maximum attenuation is based on the SNR variability.

10. A method for noise suppression, the method comprising the steps of:

estimating an amount of variability in background noise in a speech-plus-noise signal;

determining an SNR gain threshold that is a function of the amount of variability in the background noise in a speech-plus-noise signal; and

adjusting a channel gain applied to the speech-plus noise signal based on the SNR gain threshold, wherein the SNR gain threshold is the value of a channel SNR where the channel gain begins to increase from a minimum value.

11. The method of claim 10 farther comprising the step of:

attenuating the speech-plus-noise signal a first amount when the SNR variability is high, otherwise attenuating the speech-plus-noise signal a second amount.

12. The method of claim 10 wherein the step of adjusting the gain comprises the step of attenuating the speech-plus-noise signal a first amount when the variability in background noise is high, otherwise attenuating the speech-plus-noise signal a second amount.

13. The method of claim 10 wherein the step of adjusting the gain comprises the step of adjusting a gain in the speech-plus-noise signal by increasing a signal-to-noise (SNR) threshold when there exists a high variability in the background noise, wherein the speech-plus-noise signal will have a maximum attenuation when the SNR value of the speech-plus-noise signal is below the SNR threshold.

14. The method of claim 10 wherein the channel gain (γ

_DB(i)) is adjusted according to the relations;

γ

_DB(i)=μ

_g(σ

_q″

(i)−

σ

_th(σ

_n))+γ

_n

and

γ

_n≦

γ

_DB()≦

0

where

μ

_g is a gain slope,

σ

_q″

is the channel SNR for channel i,

σ

_th(σ

_n is the SNR gain threshold as a function of the background noise variability σ

_n,

γ

_n is a minimum overall gain.