Noisy speech autoregression parameter enhancement method and apparatus

• US 6,324,502 B1
• Filed: 01/09/1997
• Issued: 11/27/2001
• Est. Priority Date: 02/01/1996
• Status: Expired due to Term

• Current Assignee: Telefonaktiebolaget LM Ericsson
• Original Assignee: Telefonaktiebolaget LM Ericsson
• Inventors: Handel, Peter, Sörqvist, Patrik
• Primary Examiner(s): Hudspeth, David R.
• Assistant Examiner(s): ZINTEL, HAROLD ALBERT
• Application Number:
  US08/781,515
• Time in Patent Office: 1,783 Days
• Field of Search: 704/226, 704/227, 704/228
• US Class Current: 704/226
• CPC Class Codes: G10L 21/0208 Noise filtering

Abstract

Noisy speech parameters are enhanced by determining a background noise power spectral density (PSD) estimate, determining noisy speech parameters, determining a noisy speech PSD estimate from the speech parameters, subtracting a background noise PSD estimate from the noisy speech PSD estimate, and estimating enhanced speech parameters from the enhanced speech PSD estimate.

Claims

1. A noisy speech parameter enhancement method, comprising the steps of

receiving background noise samples and noisy speech samples;

determining a background noise power spectral density estimate at M frequencies, where M is a predetermined positive integer, from a first collection of background noise samples;

estimating p autoregressive parameters, where p is a predetermined positive integer significantly smaller than M, and a first residual variance from a second collection of noisy speech samples;

determining a noisy speech power spectral density estimate at said M frequencies from said p autoregressive parameters and said first residual variance;

determining an enhanced speech power spectral density estimate by subtracting said background noise spectral density estimate multiplied by a predetermined positive factor from said noisy speech power spectral density estimate; and

determining r enhanced autoregressive parameters using an iterative algorithm, where r is a predetermined positive integer, and an enhanced residual variance from said enhanced speech power spectral density estimate using an iterative algorithm.

2. The method of claim 1, including the step of restricting said enhanced speech power spectral density estimate to non-negative values.

3. The method of claim 2, wherein said predetermined positive factor has a value in the range 0-4.

4. The method of claim 3, wherein said predetermined positive factor is approximately equal to 1.

5. The method of claim 4, wherein said predetermined integer r is equal to said predetermined integer p.

6. The method of claim 5, including the steps of

estimating q autoregressive parameters, where q is a predetermined positive integer smaller than p, and a second residual variance from said first collection of background noise samples;

determining said background noise power spectral density estimate at said M frequencies from said q autoregressive parameters and said second residual variance.

7. The method of claim 6, including the step of averaging said background noise power spectral density estimate over a predetermined number of collections of background noise samples.

8. The method of claim 1 including the step of averaging said background noise power spectral density estimate over a predetermined number of collections of background noise samples.

9. The method of claim 1, including the step of using said enhanced autoregressive parameters and said enhanced residual variance for adjusting a filter for filtering a third collection of noisy speech samples.

10. The method of claim 9, wherein said second and said third collection of noisy speech samples are formed by the same collection.

11. The method of claim 10, including the step of Kalman filtering said third collection of noisy speech samples.

12. The method of claim 9, including the step of Kalman filtering said third collection of noisy speech samples.

13. A noisy speech parameter enhancement apparatus, comprising

means for receiving background noise samples and noisy speech samples;

means for determining a background noise power spectral density estimate at M frequencies, where M is a predetermined positive integer, from a first collection of background noise samples;

means for estimating p autoregressive parameters, where p is a predetermined positive integer significantly smaller the M, and a first residual variance from a second collection of noisy speech samples;

means for determining a noisy speech power spectral density estimate at said M frequencies from said p autoregressive parameters and said first residual variance;

means for determining an enhanced speech power spectral density estimate by subtracting said background noise spectral density estimate multiplied by a predetermined factor from said noisy speech power spectral density estimate using an iterative algorithm; and

means for determining r enhanced autoregressive parameters using an iterative algorithm, where r is a predetermined positive integer, and an enhanced residual variance from said enhanced speech power spectral density.

14. The apparatus of claim 13, including means for restricting said enhanced speech power spectral density estimate to non-negative values.

15. The apparatus of claim 14, including

means for estimating q autoregressive parameters, where q is a predetermined positive integer smaller than p, and a second residual variance from said first collection of background noise samples;

means for determining said background noise power spectral density estimate at said M frequencies from said q autoregressive parameters and said second residual variance.

16. The apparatus of claim 15, including means for averaging said background noise power spectral density estimate over a predetermined number of collections of background noise samples.

17. The apparatus of claim 13, including means for averaging said background noise power spectral density estimate over a predetermined number of collections of background noise samples.

18. The apparatus of claim 13, including means for using said enhanced autoregressive parameters and said enhanced residual variance for adjusting a filter for filtering a third collection of noisy speech samples.

19. The apparatus of claim 18, including a Kalman filter for filtering said third collection of noisy speech samples.

20. The apparatus of claim 18, including a Kalman filter for filtering said third collection of noisy speech samples, said second and said third collection of noisy speech samples being being the same collection.