Sound field spatial stabilizer with spectral coherence compensation

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.

The invention claimed is: 
     
       1. A computer implemented method for maintaining spatial stability of a sound field comprising:
 calculating one or more balance gains for two or more microphone signals, where each of the two or more microphone signals is from a corresponding one of two or more microphones, the one or more balance gains represent a detected balance of a spatial image of the sound field received by the microphones; 
 calculating one or more signal values for each of the two or more microphone signals, where the one or more signal values is characterized as a background noise estimate or one or more signal gains associated with an echo cancellation or noise reduction process; 
 calculating a pair-wise spectral coherence between each of the two or more microphone signals; and 
 maintaining the detected balance of the spatial image of the sound field received at the microphones by gain adjusting the two or more microphone signals responsive to the one or more 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 noise reduction process is associated with a transient noise. 
     
     
       3. The computer implemented method of  claim 2  where the noise reduction process is associated with a continuous noise. 
     
     
       4. The computer implemented method of  claim 1 , where the noise reduction process comprises any one or more of a wind 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 a 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 rescaled 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 one or more balance gains for two or more microphone signals, where each of the two or more microphone signals is from a corresponding one of two or more microphones, the one or more balance gains represent a detected balance of a spatial image of the sound field received by the microphones; 
 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, where the one or more signal values is characterized as a noise estimate or one or more signal gains associated with an echo cancellation or noise reduction process; 
 a coherence calculator to calculate a pair-wise spectral coherence between each of the two or more microphone signals; and 
 a gain adjuster to maintain the detected balance of the spatial image of the sound field received at the microphones though gain adjustment of the two or more microphone signals responsive to the one or more 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 a calculated suppression gain. 
     
     
       14. The system for maintaining spatial stability of a sound field of  claim 13  where the calculated 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 12 , where the noise reduction process 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 the gain adjustment of the two or more microphone signals responsive to an increased pair-wise spectral coherence includes reduction of a 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 the gain adjustment of 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 configured to mix 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.