MICROPHONE ARRAY SUBSET SELECTION FOR ROBUST NOISE REDUCTION

• US 20120051548A1
• Filed: 02/17/2011
• Published: 03/01/2012
• Est. Priority Date: 02/18/2010
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Visser, Erik, Liu, Ernan
• Granted Patent: US 8,897,455 B2
• Time in Patent Office: Days
• US Class Current: 381/56
• CPC Class Codes: G10L 2021/02166 Microphone arrays; Beamforming
• 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 disclosed method selects a plurality of fewer than all of the channels of a multichannel signal, based on information relating to the direction of arrival of at least one frequency component of the multichannel signal.

Claims

1. A method of processing a multichannel signal, said method comprising:

for each of a plurality of different frequency components of the multichannel signal, calculating a difference between a phase of the frequency component at a first time in each of a first pair of channels of the multichannel signal, to obtain a first plurality of phase differences;

based on information from the first plurality of calculated phase differences, calculating a value of a first coherency measure that indicates a degree to which the directions of arrival of at least the plurality of different frequency components of the first pair at the first time are coherent in a first spatial sector;

for each of the plurality of different frequency components of the multichannel signal, calculating a difference between a phase of the frequency component at a second time in each of a second pair of channels of the multichannel signal, said second pair being different than said first pair, to obtain a second plurality of phase differences;

based on information from the second plurality of calculated phase differences, calculating a value of a second coherency measure that indicates a degree to which the directions of arrival of at least the plurality of different frequency components of the second pair at the second time are coherent in a second spatial sector;

calculating a contrast of the first coherency measure by evaluating a relation between the calculated value of the first coherency measure and an average value of the first coherency measure over time;

calculating a contrast of the second coherency measure by evaluating a relation between the calculated value of the second coherency measure and an average value of the second coherency measure over time; and

based on which among the first and second coherency measures has the greatest contrast, selecting one among the first and second pairs of channels.

2. The method according to claim 1, wherein said selecting one among the first and second pairs of channels is based on (A) a relation between an energy of each of the first pair of channels and on (B) a relation between an energy of each of the second pair of channels.

3. The method according to claim 1, wherein said method comprises, in response to said selecting one among the first and second pairs of channels, calculating an estimate of a noise component of the selected pair.

4. The method according to claim 1, wherein said method comprises, for at least one frequency component of at least one channel of the selected pair, attenuating the frequency component, based on the calculated phase difference of the frequency component.

5. The method according to claim 1, wherein said method comprises estimating a range of a signal source, and

wherein said selecting one among the first and second pairs of channels is based on said estimated range.

6. The method according to claim 1, wherein each of said first pair of channels is based on a signal produced by a corresponding one of a first pair of microphones, and

wherein each of said second pair of channels is based on a signal produced by a corresponding one of a second pair of microphones.

7. The method according to claim 6, wherein the first spatial sector includes an endfire direction of the first pair of microphones and the second spatial sector includes an endfire direction of the second pair of microphones.

8. The method according to claim 6, wherein the first spatial sector excludes a broadside direction of the first pair of microphones and the second spatial sector excludes a broadside direction of the second pair of microphones.

9. The method according to claim 6, wherein the first pair of microphones includes one among the second pair of microphones.

10. The method according to claim 6, wherein a position of each among the first pair of microphones is fixed relative to a position of the other among the first pair of microphones, and

wherein at least one among the second pair of microphones is movable relative to the first pair of microphones.

11. The method according to claim 6, wherein said method comprises receiving at least one among the second pair of channels via a wireless transmission channel.

12. The method according to claim 6, wherein said selecting one among the first and second pairs of channels is based on (A) a relation between (A) an energy of the first pair of channels in a beam that includes one endfire direction of the first pair of microphones and excludes the other endfire direction of the first pair of microphones and (B) an energy of the second pair of channels in a beam that includes one endfire direction of the second pair of microphones and excludes the other endfire direction of the second pair of microphones.

13. The method according to claim 6, wherein said method comprises:

estimating a range of a signal source; and

at a third time subsequent to the first and second times, and based on said estimated range, selecting another among the first and second pairs of channels based on (A) a relation between (A) an energy of the first pair of channels in a beam that includes one endfire direction of the first pair of microphones and excludes the other endfire direction of the first pair of microphones and (B) an energy of the second pair of channels in a beam that includes one endfire direction of the second pair of microphones and excludes the other endfire direction of the second pair of microphones.

14. A computer-readable storage medium having tangible features that cause a machine reading the features to perform a method according to claim 1.

15. An apparatus for processing a multichannel signal, said apparatus comprising:

means for calculating, for each of a plurality of different frequency components of the multichannel signal, a difference between a phase of the frequency component at a first time in each of a first pair of channels of the multichannel signal, to obtain a first plurality of phase differences;

means for calculating a value of a first coherency measure, based on information from the first plurality of calculated phase differences, that indicates a degree to which the directions of arrival of at least the plurality of different frequency components of the first pair at the first time are coherent in a first spatial sector;

means for calculating, for each of the plurality of different frequency components of the multichannel signal, a difference between a phase of the frequency component at a second time in each of a second pair of channels of the multichannel signal, said second pair being different than said first pair, to obtain a second plurality of phase differences;

means for calculating a value of a second coherency measure, based on information from the second plurality of calculated phase differences, that indicates a degree to which the directions of arrival of at least the plurality of different frequency components of the second pair at the second time are coherent in a second spatial sector;

means for calculating a contrast of the first coherency measure by evaluating a relation between the calculated value of the first coherency measure and an average value of the first coherency measure over time;

means for calculating a contrast of the second coherency measure by evaluating a relation between the calculated value of the second coherency measure and an average value of the second coherency measure over time; and

means for selecting one among the first and second pairs of channels, based on which among the first and second coherency measures has the greatest contrast.

16. The apparatus according to claim 15, wherein said means for selecting one among the first and second pairs of channels is configured to select said one among the first and second pairs of channels based on (A) a relation between an energy of each of the first pair of channels and on (B) a relation between an energy of each of the second pair of channels.

17. The apparatus according to claim 15, wherein said apparatus comprises means for calculating, in response to said selecting one among the first and second pairs of channels, an estimate of a noise component of the selected pair.

18. The apparatus according to claim 15, wherein each of said first pair of channels is based on a signal produced by a corresponding one of a first pair of microphones, and

wherein each of said second pair of channels is based on a signal produced by a corresponding one of a second pair of microphones.

19. The apparatus according to claim 18, wherein the first spatial sector includes an endfire direction of the first pair of microphones and the second spatial sector includes an endfire direction of the second pair of microphones.

20. The apparatus according to claim 18, wherein the first spatial sector excludes a broadside direction of the first pair of microphones and the second spatial sector excludes a broadside direction of the second pair of microphones.

21. The apparatus according to claim 18, wherein the first pair of microphones includes one among the second pair of microphones.

22. The apparatus according to claim 18, wherein a position of each among the first pair of microphones is fixed relative to a position of the other among the first pair of microphones, and

wherein at least one among the second pair of microphones is movable relative to the first pair of microphones.

23. The apparatus according to claim 18, wherein said apparatus comprises means for receiving at least one among the second pair of channels via a wireless transmission channel.

24. The apparatus according to claim 18, wherein said means for selecting one among the first and second pairs of channels is configured to select said one among the first and second pairs of channels based on (A) a relation between (A) an energy of the first pair of channels in a beam that includes one endfire direction of the first pair of microphones and excludes the other endfire direction of the first pair of microphones and (B) an energy of the second pair of channels in a beam that includes one endfire direction of the second pair of microphones and excludes the other endfire direction of the second pair of microphones.

25. An apparatus for processing a multichannel signal, said apparatus comprising:

a first calculator configured to calculate, for each of a plurality of different frequency components of the multichannel signal, a difference between a phase of the frequency component at a first time in each of a first pair of channels of the multichannel signal, to obtain a first plurality of phase differences;

a second calculator configured to calculate a value of a first coherency measure, based on information from the first plurality of calculated phase differences, that indicates a degree to which the directions of arrival of at least the plurality of different frequency components of the first pair at the first time are coherent in a first spatial sector;

a third calculator configured to calculate, for each of the plurality of different frequency components of the multichannel signal, a difference between a phase of the frequency component at a second time in each of a second pair of channels of the multichannel signal, said second pair being different than said first pair, to obtain a second plurality of phase differences;

a fourth calculator configured to calculate a value of a second coherency measure, based on information from the second plurality of calculated phase differences, that indicates a degree to which the directions of arrival of at least the plurality of different frequency components of the second pair at the second time are coherent in a second spatial sector;

a fifth calculator configured to calculate a contrast of the first coherency measure by evaluating a relation between the calculated value of the first coherency measure and an average value of the first coherency measure over time;

a sixth calculator configured to calculate a contrast of the second coherency measure by evaluating a relation between the calculated value of the second coherency measure and an average value of the second coherency measure over time; and

a selector configured to select one among the first and second pairs of channels, based on which among the first and second coherency measures has the greatest contrast.

26. The apparatus according to claim 25, wherein said selector is configured to select said one among the first and second pairs of channels based on (A) a relation between an energy of each of the first pair of channels and on (B) a relation between an energy of each of the second pair of channels.

27. The apparatus according to claim 25, wherein said apparatus comprises a seventh calculator configured to calculate, in response to said selecting one among the first and second pairs of channels, an estimate of a noise component of the selected pair.

28. The apparatus according to claim 25, wherein each of said first pair of channels is based on a signal produced by a corresponding one of a first pair of microphones, and

wherein each of said second pair of channels is based on a signal produced by a corresponding one of a second pair of microphones.

29. The apparatus according to claim 28, wherein the first spatial sector includes an endfire direction of the first pair of microphones and the second spatial sector includes an endfire direction of the second pair of microphones.

30. The apparatus according to claim 28, wherein the first spatial sector excludes a broadside direction of the first pair of microphones and the second spatial sector excludes a broadside direction of the second pair of microphones.

31. The apparatus according to claim 28, wherein the first pair of microphones includes one among the second pair of microphones.

32. The apparatus according to claim 28, wherein a position of each among the first pair of microphones is fixed relative to a position of the other among the first pair of microphones, and

wherein at least one among the second pair of microphones is movable relative to the first pair of microphones.

33. The apparatus according to claim 28, wherein said apparatus comprises a receiver configured to receive at least one among the second pair of channels via a wireless transmission channel.

34. The apparatus according to claim 28, wherein said selector is configured to select said one among the first and second pairs of channels based on (A) a relation between (A) an energy of the first pair of channels in a beam that includes one endfire direction of the first pair of microphones and excludes the other endfire direction of the first pair of microphones and (B) an energy of the second pair of channels in a beam that includes one endfire direction of the second pair of microphones and excludes the other endfire direction of the second pair of microphones.