MIXER WITH ADAPTIVE POST-FILTERING

• US 20090116661A1
• Filed: 11/04/2008
• Published: 05/07/2009
• Est. Priority Date: 11/05/2007
• Status: Active Grant

• Current Assignee: Malikie Innovations Limited (Key Patent Innovations Limited)
• Original Assignee: QNX Software Systems Wavemakers Inc (Blackberry Limited)
• Inventors: Hetherington, Phillip A.
• Granted Patent: US 8,121,311 B2
• Time in Patent Office: Days
• US Class Current: 381/93
• CPC Class Codes: G10K 11/16 Methods or devices for protecting against, or for damping, noise or other acoustic waves in general G10K11/36 takes precedence
• CPC Class Codes: G10L 19/26 Pre-filtering or post-filtering
• CPC Class Codes: G10L 2021/02165 Two microphones, one receiving mainly the noise signal and the other one mainly the speech signal
• CPC Class Codes: G10L 21/02 Speech enhancement, e.g. noise reduction or echo cancellation reducing echo effects in line transmission systems H04B3/20; echo suppression in hands-free telephones H04M9/08
• CPC Class Codes: G10L 21/0208 Noise filtering
• CPC Class Codes: H04R 3/005 for combining the signals of two or more microphones specially adapted for hearing aids H04R25/407

Abstract

A noise reduction system includes multiple transducers that generate time domain signals. A transforming device transforms the time domain signals into frequency domain signals. A signal mixing device mixes the frequency domain signals according to a mixing ratio. Frequency domain signals are rotated in phase to generate phase rotated signals. A post-processing device attenuates portions of the output based on coherence levels of the signals.

Claims

1. A noise reduction system, comprising:

a plurality of transducers configured to generate time domain signals;

a transforming device configured to transform the time domain signals into frequency domain signals;

a signal mixing device configured to mix the frequency domain signals according to a mixing ratio based on a magnitude and a signal-to-noise ratio of the frequency domain signals;

the mixing device configured to rotate respective frequency domain signals in phase to generate corresponding phase rotated signals, and add the phase rotated signals based on the mixing ratio to generate an output; and

a post-processing device configured to attenuate portions of the output based on coherence levels of the respective frequency domain signals.

2. The noise reduction system of claim 1 where the plurality of transducers comprises a plurality of devices that convert sound into analog or digital signals.

3. The noise reduction system of claim 1 where the signal mixing device comprises a comparator that compares the magnitude of the frequency domain signals to a noise estimate.

4. The noise reduction system of claim 1 where the mixing device is further configured to estimate the phase differences between the frequency domain signals.

5. The noise reduction system of claim 4 where the phase difference is stored in a distributed memory.

6. The noise reduction system of claim 5 where the mixing ratio comprises a ratio of the magnitudes of the frequency domain signals.

7. The noise reduction system of claim 6 where the mixing ratio is a time smoothed ratio.

8. The noise reduction system of claim 7 where the time smoothed ratio is a variable ratio that varies with signal frequency.

9. The noise reduction system of claim 7 further comprising a wind buffet detection device configured to identify noises associated with wind flow.

10. The noise reduction system of claim 9 further comprising a wind buffet suppression device configured to dampen the noises associated identify with wind flow.

11. The noise reduction system of claim 1 where the post-processing device attenuates portions of the output based on a user programmed element.

12. The noise reduction system of claim 1 where the post-processing device comprises a coherence edge enhancement device.

13. The noise reduction system of claim 12 where the post-processing device attenuates spectral coherence between neighboring harmonics.

14. The noise reduction system of claim 1 where the coherence comprises a normalized coherence that accounts for maximum and minimum coherence.

15. The noise reduction system of claim 1 where the mixing device comprises an echo cancellation system.

16. The noise reduction system of claim 1 where the mixing device and post-processing device interfaces a vehicle.

17. A noise reduction system, comprising:

a transforming device configured to transform time domain signals into frequency domain signals;

means to mix the frequency domain signals according to a mixing ratio based on a magnitude and a signal-to-noise ratio of the frequency domain signals;

the means to mix configured to rotate respective frequency domain signals in phase to generate corresponding phase rotated signals, and add the phase rotated signals based on the mixing ratio to generate an output; and

a processor configured to attenuate portions of the output based on coherence levels of the respective frequency domain signals.

18. The noise reduction system of claim 17 where the means to mix is further configured to estimate the phase differences between the frequency domain signals.

19. The noise reduction system of claim 18 where the phase difference is stored in a distributed memory remote from the means to mix.

20. The noise reduction system of claim 19 where the mixing ratio comprises a ratio of the magnitudes of the frequency domain signals.

21. The noise reduction system of claim 20 where the mixing ratio is a time smoothed ratio.

22. The noise reduction system of claim 21 where the time smoothed ratio is a variable ratio that varies with signal frequency.

23. The noise reduction system of claim 21 further comprising a wind buffet detection device configured to identify noises associated with wind flow.

24. The noise reduction system of claim 23 further comprising a wind buffet suppression device configured to dampen the noises associated identify with wind flow.