Noise reduction system

• US 5,012,519 A
• Filed: 01/05/1990
• Issued: 04/30/1991
• Est. Priority Date: 12/25/1987
• Status: Expired due to Term

• Current Assignee: DSP Group Incorporated (Synaptics Incorporated)
• Original Assignee: DSP Group Incorporated (Synaptics Incorporated)
• Inventors: Stettiner, Yoram, Berstein, Alberto, Adlersberg, Shabtai, Aizner, Mendel
• Primary Examiner(s): Kemeny, Emanuel S.
• Application Number:
  US07/463,950
• Time in Patent Office: 480 Days
• Field of Search: 381/47, 381/46
• US Class Current: 704/226
• CPC Class Codes: G10L 2021/02168 the estimation exclusively taking place during speech pauses
• CPC Class Codes: G10L 21/0208 Noise filtering
• CPC Class Codes: G10L 21/0232 Processing in the frequency domain

Abstract

Noise in a speech-plus-noise input signal is suppressed by splitting the input signal into spectral channels and decreasing the gain in the each channel which has a low signal-to-noise ratio (SNR). A voice operated switch (VOX) acts to detect noise-only input to gate a background noise (input signal) estimator and also to gate a residual noise (output signal) estimator. The gain in each of the channels is controlled by the current value (a posteriori) input signal SNR estimate, modified by the prior value (a priori) input signal SNR estimate, and smoothed as a function of the residual (output noise signal) estimate.

Claims

1. A digital processing method for reducing the noise in noisy speech signals, including the steps of:

(a) generating background noise estimates from noisy speech and storing said background noise estimates;

(b) generating adaptive current noise estimates from current noisy speech signals and stored background noise estimates;

(c) generating current gain estimates from adaptive current noise estimates and past speech estimates; and

(d) using current gain estimates and current noisy speech to obtain current speech estimates,

wherein said step of using adaptive current noise estimates and past speech estimates to obtain current gain estimates includes the step of limiting the lower limit of the gain estimate to eliminate musical noise, and

wherein said step of generating adaptive current noise estimates includes employing results of a speech/no speech decision from information obtained from current signal input to distinguish said noisy speech from background noise.

2. A digital processing method according to claim 1 and wherein said step of using current gain estimates and current noisy speech to obtain current speech estimates comprise the step of applying an automatic gain control algorithm to estimated speech in order to restore the original energy envelope of the speech.

3. The digital method of claims 1 or 2 and wherein said current noise estimates are background noise estimates.

4. The invention of claim 1 further including the step of using a speech, no speech decision to select an algorithm when generating decision directed estimates.

5. A digital processing method for reducing the noise in noisy speech signal, comprising the steps of:

(a) generating amplitude estimates from noisy speech;

(b) generating residual noise estimates from said amplitude estimates by operation of a voice operated switch; and

(c) generating adaptive residual noise estimates from said amplitude estimates when speech is not present; and

(d) using said adaptive residual noise estimates for smoothing speech signals.

6. A method for reducing the noise in noisy signals containing speech, said method comprising the steps of:

(a) generating, from Fourier expansion coefficients of said noisy signals, background noise estimates, and storing said background noise estimates;

(b) generating thereafter, from Fourier expansion coefficients of said signals and said stored background noise estimates, adaptive current noise estimates;

(c) generating thereafter, from said adaptive current noise estimates and past speech estimates, current gain estimates; and

(d) producing thereafter, from said current gain estimates and current digitized noisy signals, current speech estimates, said current speech estimates for use thereafter as past speech estimates,

wherein said step (c) includes the step of limiting the lower limit of said gain estimate to eliminate musical noise, and

wherein said step (b) includes applying a speech/no speech decision to said noisy signals containing speech to identify said current speech estimates with a signal segment containing speech.

7. A method for reducing noise in noisy signals containing speech, said noisy signals being divided into time invariant segments, said method including the steps of:

(a) generating, from Fourier expansion coefficients of said segments of said noisy signals, amplitude estimates;

(b) thereafter generating, from said amplitude estimates, (i) residual noise estimates from said amplitude estimates where speech is present in a current segment, and (ii) adaptive residual noise estimates where speech is not present in a current segment; and

(e) smoothing said noisy signal containing speech with said adaptive residual noise estimates to suppress noise.

8. A digital processing method for reducing the noise in noisy speech signals, including the steps of:

(a) generating, from Fourier expansion coefficients of segments of said noisy speech signals as amplitude estimates;

(b) generating background noise estimates from said amplitude estimates, including employing results of a speech/no speech decision (Y/N) from information obtained from current signal input to distinguish signals containing speech from background noise;

(c) generating first signal-to-noise estimates from said background noise estimates and said amplitude estimates (a posteriori SNR);

(d) generating decision directed signal-to-noise estimates recursively from said background noise estimates updated on the basis of previous speech amplitude estimates (a priori SNR);

(e) generating current gain estimates from said first signal-to-noise estimate and said decision directed signal-to-noise estimates; and

(e) using current gain estimates and current noisy speech to obtain current speech amplitude estimates.

9. The method according to claim 8 wherein said step of using current estimates further includes the step of limiting the gain estimates to gain limited estimates to eliminate musical noise.

10. The method according to claim 8 further including the steps of employing said current speech amplitude estimates using current estimates and results of a speech/no speech decision (Y/N) from information obtained from current signal input to generate a threshold signal for adaptive residual noise for obtaining smoothed amplitude estimates.