SOUND FIELD SPATIAL STABILIZER WITH SPECTRAL COHERENCE COMPENSATION

• US 20140376742A1
• Filed: 06/20/2013
• Published: 12/25/2014
• Est. Priority Date: 06/20/2013
• Status: Active Grant

• Current Assignee: Blackberry Limited
• Original Assignee: QNX Software Systems Limited (Canada) (Blackberry Limited)
• Inventors: Hetherington, Phillip Alan
• Granted Patent: US 9,271,100 B2
• Time in Patent Office: Days
• US Class Current: 381/94.2
• CPC Class Codes: H04R 2430/01 Aspects of volume control, not necessarily automatic, in sound systems
• CPC Class Codes: H04R 2430/03 Synergistic effects of band splitting and sub-band processing
• CPC Class Codes: H04R 29/004 for microphones H04R29/007 takes precedence
• CPC Class Codes: H04R 3/005 for combining the signals of two or more microphones specially adapted for hearing aids H04R25/407
• CPC Class Codes: H04S 7/00 Indicating arrangements; Control arrangements, e.g. balance control

Abstract

In a system and method for maintaining the spatial stability of a sound field a balance gain may be calculated for two or more microphone signals. The balance gain may be associated with a spatial image in the sound field. Signal values may be calculated for each of the microphone. The signal values may be signal estimates or signal gains calculated to improve a characteristic of the microphone signals. The differences between the signal values associated with each microphone signal may be limited although some difference between signal values may be allowable. One or more microphone signals are adjusted responsive to the two or more balance gains and the signal gains to maintain the spatial stability of the sound field. The adjustments of one or more microphone signals may include mixing of two or more microphone. The signal gains are applied to the two or more microphone signals.

Claims

1. A computer implemented method for maintaining spatial stability of a sound field comprising:

calculating balance gains for each of two or more microphone signals;

calculating one or more signal values for each of the two or more microphone signals;

calculating a pair-wise spectral coherence between each of the two or more microphone signals; and

gain adjusting the two or more microphone signals responsive to the calculated balance gains, the one or more signal values, and the pair-wise spectral coherence for each of the two or more microphone signals.

2. The computer implemented method of claim 1, where the one or more signal values comprises one or more of an estimated background noise and a calculated suppression gain.

3. The computer implemented method of claim 2 where calculating the suppression gain comprises one or more of a noise reduction calculation and an echo cancellation calculation.

4. The computer implemented method of claim 3, where the noise reduction calculation comprises any one or more of a wind noise reduction calculation, transients noise reduction calculation, road noise reduction calculation, repetitive noise reduction calculation and engine noise reduction calculation.

5. The computer implemented method of claim 1, where gain adjusting the two or more microphone signals responsive to an increased pair-wise spectral coherence includes reducing the suppression gain for a higher amplitude microphone signal of the two or more microphone signals.

6. The computer implemented method of claim 5, where the increased pair-wise spectral coherence is greater than about 0.85.

7. The computer implemented method of claim 6, where a pair-wise spectral coherence range between about 0.85 and about 1.0 is resealed to between 0 and about 1.

8. The computer implemented method of claim 1, where gain adjusting the two or more microphone signals responsive to an increased pair-wise spectral coherence increases the balance gain of a lower amplitude microphone signal of the two or more microphone signals.

9. The computer implemented method of claim 1, further comprising mixing two or more gain adjusted microphone signals together.

10. The computer implemented method of claim 1, further comprising generating a set of sub-bands for each of the two or more microphone signals using a subband filter or a Fast Fourier Transform.

11. The computer implemented method of claim 1, further comprising generating a set of sub-bands for each of the two or more microphone signals according to a critical, octave, mel, or bark band spacing technique.

12. A system for maintaining spatial stability of a sound field comprising:

a balance calculator to calculate balance gains for each of two or more microphone signals;

two or more signal value generators, each one associated with one of the two or more microphone signals, to calculate one or more signal values;

a coherence calculator to calculate a pair-wise spectral coherence between each of the two or more microphone signals; and

a gain adjuster to gain adjust the two or more microphone signals responsive to the calculated balance gains, the one or more signal values, and the pair-wise spectral coherence for each of the two or more microphone signals.

13. The system for maintaining spatial stability of a sound field of claim 12, where the one or more signal values comprises one or more of an estimated background noise and a calculated suppression gain.

14. The system for maintaining spatial stability of a sound field of claim 13 where calculating the suppression gain comprises one or more of a noise reduction calculation and an echo cancellation calculation.

15. The system for maintaining spatial stability of a sound field of claim 14, where the noise reduction calculation comprises any one or more of a wind noise reduction calculation, transients noise reduction calculation, a road noise reduction calculation, a repetitive noise reduction calculation and an engine noise reduction calculation.

16. The system for maintaining spatial stability of a sound field of claim 12, where gain adjusting the two or more microphone signals responsive to an increased pair-wise spectral coherence includes reducing the suppression gain for a higher amplitude microphone signal of the two or more microphone signals.

17. The system for maintaining spatial stability of a sound field of claim 16, where the increased pair-wise spectral coherence is greater than about 0.85.

18. The system for maintaining spatial stability of a sound field of claim 17, where a pair-wise spectral coherence range between about 0.85 and about 1.0 is rescaled to between 0 and about 1.

19. The system for maintaining spatial stability of a sound field of claim 12, where gain adjusting the two or more microphone signals responsive to an increased pair-wise spectral coherence increases the balance gain of a lower amplitude microphone signal of the two or more microphone signals.

20. The system for maintaining spatial stability of a sound field of claim 12, further comprising a mixer for mixing two or more gain adjusted microphone signals together.

21. The system for maintaining spatial stability of a sound field of claim 12, further comprising means for generating a set of sub-bands for each of the two or more microphone signals using a subband filter or a Fast Fourier Transform.

22. The system for maintaining spatial stability of a sound field of claim 12, further comprising means for generating a set of sub-bands for each of the two or more microphone signals according to a critical, octave, mel, or bark band spacing technique.