Adaptive close-talking differential microphone array

• US 20030016835A1
• Filed: 10/30/2001
• Published: 01/23/2003
• Est. Priority Date: 07/18/2001
• Status: Active Grant

• Current Assignee: Bell Northern Research, LLC (Hilco Inc. (d/b/a Hilco Global))
• Original Assignee: Agere Systems Incorporated (Broadcom, Inc.)
• Inventors: Elko, Gary W., Teutsch, Heinz
• Granted Patent: US 7,123,727 B2
• Time in Patent Office: Days
• US Class Current: 381/92
• CPC Class Codes: H04R 1/406 microphones
• CPC Class Codes: H04R 29/006 Microphone matching
• CPC Class Codes: H04R 3/005 for combining the signals of two or more microphones specially adapted for hearing aids H04R25/407

Abstract

A method and apparatus for providing a differential microphone with a desired frequency response are disclosed. The desired frequency response is provided by operation of a filter, having an adjustable frequency response, coupled to the microphone. The frequency response of the filter is set by operation of a controller, also coupled to the microphone, based on signals received from the microphone. The desired frequency response may be determined based upon the orientation angle and the distance between the microphone and a source of sound. The frequency response of the filter may comprise the substantial inverse of the frequency response of the microphone to provide a flat response. In a preferred embodiment, the gain of the differential microphone is adjusted so that the output level is effectively independent of microphone position relative to the source. In particular embodiments, the controller may determine, based on the distance from the sound source, whether to operate the differential microphone in a nearfield mode of operation or a farfield mode of operation.

Claims

1. A method for providing a differential microphone with a desired frequency response, the differential microphone coupled to a filter having a frequency response which is adjustable, the method comprising the steps of:

(a) determining an orientation angle between the differential microphone and a desired source of signal;

(b) determining a distance between the differential microphone and the desired source of signal;

(c) determining a filter frequency response, based on the determined distance and orientation angle, to provide the differential microphone with the desired frequency response to sound from the desired source; and

(d) adjusting the filter to exhibit the determined frequency response.

2. The invention of claim 1, wherein the differential microphone is a close-talking differential microphone array (CTMA).

3. The invention of claim 2, wherein the CTMA is a first-order microphone array.

4. The invention of claim 1, wherein step (a) comprises the steps of:

(1) determining a time difference of arrival (TDOA) of sound from the desired source for the differential microphone; and

(2) determining the orientation angle based on the TDOA.

5. The invention of claim 4, wherein the distance is determined based on the determined orientation angle.

6. The invention of claim 1, wherein the distance is determined based on the determined orientation angle.

7. The invention of claim 1, further comprising the step of performing a calibration procedure to compensate for differences between elements in the differential microphone.

8. The invention of claim 7, wherein the calibration procedure comprises the steps of:

(1) minimizing mean squared error of differential microphone signals corresponding to a farfield broadband audio source positioned at broadside with respect to the differential microphone;

(2) selecting coefficients for a calibration filter when power of the minimized mean squared error falls below a specified threshold level; and

(3) filtering the differential microphone signals using the calibration filter to compensate for the differences between the elements in the differential microphone.

9. The invention of claim 1, wherein steps (c) and (d) are implemented only after determining that the determined distance is not greater than a specified threshold distance.

10. The invention of claim 9, wherein the differential microphone is operated in a farfield mode of operation after determining that the determined distance is greater than the specified threshold distance.

11. The invention of claim 1, further comprising the step of adjusting gain of the differential microphone.

12. The invention of claim 11, wherein adjustments to the gain are based on the determined orientation angle and the determined distance.

13. The invention of claim 1, wherein the determined angle and the determined distance are quantized to form a set of quantized parameters, wherein the filter is adjusted only when the set of quantized parameters changes.

14. The invention of claim 1, wherein:

the differential microphone is a first-order close-talking differential microphone array (CTMA);

step (a) comprises the steps of;

(1) determining a time difference of arrival (TDOA) of sound from the desired source for the differential microphone; and

(2) determining the orientation angle based on the TDOA;

the distance is determined based on the determined orientation angle;

further comprising the step of performing a calibration procedure to compensate for differences between elements in the differential microphone;

the calibration procedure comprises the steps of;

(1) minimizing mean squared error of differential microphone signals corresponding to a farfield broadband audio source positioned at broadside with respect to the differential microphone;

(2) selecting coefficients for a calibration filter when power of the minimized mean squared error falls below a specified threshold level; and

(3) filtering the differential microphone signals using the calibration filter to compensate for the differences between the elements in the differential microphone;

steps (c) and (d) are implemented only after determining that the determined distance is not greater than a specified threshold distance;

the differential microphone is operated in a farfield mode of operation after determining that the determined distance is greater than the specified threshold distance;

further comprising the step of adjusting gain of the differential microphone, wherein adjustments to the gain are based on the determined orientation angle and the determined distance; and

the determined angle and the determined distance are quantized to form a set of quantized parameters, wherein the filter is adjusted only when the set of quantized parameters changes.

16. The invention of claim 15, wherein the differential microphone is a close-talking differential microphone array (CTMA).

17. The invention of claim 16, wherein the CTMA is a first-order microphone array.

18. The invention of claim 15, wherein the controller is configured to:

(1) determine a time difference of arrival (TDOA) of sound from the desired source for the differential microphone; and

(2) determine the orientation angle based on the TDOA.

19. The invention of claim 18, wherein the distance is determined based on the determined orientation angle.

20. The invention of claim 15, wherein the distance is determined based on the determined orientation angle.

21. The invention of claim 15, wherein the controller is configured to perform a calibration procedure to compensate for differences between elements in the differential microphone.

22. The invention of claim 21, wherein the calibration procedure comprises the steps of:

(1) minimizing mean squared error of differential microphone signals corresponding to a farfield broadband audio source positioned at broadside with respect to the differential microphone;

(2) selecting coefficients for a calibration filter when power of the minimized mean squared error falls below a specified threshold level; and

(3) filtering the differential microphone signals using the calibration filter to compensate for the differences between the elements in the differential microphone.

23. The invention of claim 15, wherein the controller adjusts the filter only after determining that the determined distance is not greater than a specified threshold distance.

24. The invention of claim 23, wherein the differential microphone is operated in a farfield mode of operation after determining that the determined distance is greater than the specified threshold distance.

25. The invention of claim 15, wherein the controller adjusts gain of the differential microphone.

26. The invention of claim 25, wherein adjustments to the gain are based on the determined orientation angle and the determined distance.

27. The invention of claim 15, wherein the determined angle and the determined distance are quantized to form a set of quantized parameters, wherein the filter is adjusted only when the set of quantized parameters changes.

28. The invention of claim 15, wherein:

the differential microphone is a first-order close-talking differential microphone array (CTMA);

the controller is configured to;

(1) determine a time difference of arrival (TDOA) of sound from the desired source for the differential microphone; and

(2) determine the orientation angle based on the TDOA;

the distance is determined based on the determined orientation angle;

the controller is configured to perform a calibration procedure to compensate for differences between elements in the differential microphone;

the calibration procedure comprises the steps of;

(1) minimizing mean squared error of differential microphone signals corresponding to a farfield broadband audio source positioned at broadside with respect to the differential microphone;

(2) selecting coefficients for a calibration filter when power of the minimized mean squared error falls below a specified threshold level; and

(3) filtering the differential microphone signals using the calibration filter to compensate for the differences between the elements in the differential microphone;

the controller adjusts the filter only after determining that the determined distance is not greater than a specified threshold distance;

the differential microphone is operated in a farfield mode of operation after determining that the determined distance is greater than the specified threshold distance;

the controller adjusts gain of the differential microphone, wherein adjustments to the gain are based on the determined orientation angle and the determined distance; and

the determined angle and the determined distance are quantized to form a set of quantized parameters, wherein the filter is adjusted only when the set of quantized parameters changes.

15. An apparatus for providing a differential microphone with a desired frequency response, the apparatus comprising:

(a) an adjustable filter, coupled to the differential microphone; and

(b) a controller, coupled to the differential microphone and the filter and configured to (1) determine a distance and an orientation angle between the differential microphone and a desired source of sound and (2) adjust the filter to provide the differential microphone with the desired frequency response based on the determined distance and orientation angle.

29. A machine-readable medium, having encoded thereon program code, wherein, when the program code is executed by a machine, the machine implements a method for providing a differential microphone with a desired frequency response, the differential microphone coupled to a filter having a frequency response which is adjustable, the method comprising the steps of:

(a) determining an orientation angle between the differential microphone and a desired source of signal;

(b) determining a distance between the differential microphone and the desired source of signal;

(c) determining a filter frequency response, based on the determined distance and orientation angle, to provide the differential microphone with the desired frequency response to sound from the desired source; and

(d) adjusting the filter to exhibit the determined frequency response.

30. A method for operating a differential microphone comprising the steps of:

(a) determining a distance between the differential microphone and a desired source of signal;

(b) comparing the determined distance to a specified threshold distance;

(c) determining whether to operate the differential microphone in a nearfield mode of operation or a farfield mode of operation based on the comparison of step (b); and

(d) operating the differential microphone in the determined mode of operation.

31. The invention of claim 30, wherein the differential microphone is a first-order microphone array.

32. The invention of claim 30, wherein step (a) comprises the steps of:

(1) determining a time difference of arrival (TDOA) of sound from the desired source for the differential microphone;

(2) determining an orientation angle based on the TDOA; and

(3) determining the distance based on the determined orientation angle.

33. The invention of claim 30, wherein the nearfield mode of operation provides the differential microphone with a desired frequency response, the differential microphone coupled to a filter having a frequency response which is adjustable.

34. The invention of claim 33, wherein the nearfield mode of operation comprises the steps of:

(1) determining an orientation angle between the differential microphone and a desired source of signal;

(2) determining the distance between the differential microphone and the desired source of signal;

(3) determining a filter frequency response, based on the determined distance and orientation angle, to provide the differential microphone with the desired frequency response to sound from the desired source; and

(4) adjusting the filter to exhibit the determined frequency response.

35. The invention of claim 30, wherein:

the differential microphone is a first-order microphone array;

step (a) comprises the steps of;

(1) determining a time difference of arrival (TDOA) of sound from the desired source for the differential microphone;

(2) determining an orientation angle based on the TDOA; and

(3) determining the distance based on the determined orientation angle;

the nearfield mode of operation provides the differential microphone with a desired frequency response, the differential microphone coupled to a filter having a frequency response which is adjustable; and

the nearfield mode of operation comprises the steps of;

(1) determining an orientation angle between the differential microphone and a desired source of signal;

(2) determining the distance between the differential microphone and the desired source of signal;

(3) determining a filter frequency response, based on the determined distance and orientation angle, to provide the differential microphone with the desired frequency response to sound from the desired source; and

(4) adjusting the filter to exhibit the determined frequency response.

37. The invention of claim 36, wherein the differential microphone is a first-order microphone array.

38. The invention of claim 36, wherein step (a) comprises the steps of:

(1) determining a time difference of arrival (TDOA) of sound from the desired source for the differential microphone;

(2) determining an orientation angle based on the TDOA; and

(3) determining the distance based on the determined orientation angle.

39. The invention of claim 36, further comprising a filter having a frequency response which is adjustable, wherein the filter is coupled to the controller and configured to be coupled to the differential microphone, wherein the nearfield mode of operation provides the differential microphone with a desired frequency response, the differential microphone coupled to a filter having a frequency response which is adjustable.

40. The invention of claim 39, wherein the nearfield mode of operation comprises the steps of:

(i) determining an orientation angle between the differential microphone and a desired source of signal;

(ii) determining the distance between the differential microphone and the desired source of signal;

(iii) determining a filter frequency response, based on the determined distance and orientation angle, to provide the differential microphone with the desired frequency response to sound from the desired source; and

(iv) adjusting the filter to exhibit the determined frequency response.

41. The invention of claim 36, wherein:

the differential microphone is a first-order microphone array;

step (a) comprises the steps of;

(1) determining a time difference of arrival (TDOA) of sound from the desired source for the differential microphone;

(2) determining an orientation angle based on the TDOA; and

(3) determining the distance based on the determined orientation angle;

further comprising a filter having a frequency response which is adjustable, wherein the filter is coupled to the controller and configured to be coupled to the differential microphone, wherein the nearfield mode of operation provides the differential microphone with a desired frequency response, the differential microphone coupled to a filter having a frequency response which is adjustable; and

the nearfield mode of operation comprises the steps of;

(i) determining an orientation angle between the differential microphone and a desired source of signal;

(ii) determining the distance between the differential microphone and the desired source of signal;

(iii) determining a filter frequency response, based on the determined distance and orientation angle, to provide the differential microphone with the desired frequency response to sound from the desired source; and

(iv) adjusting the filter to exhibit the determined frequency response.

36. An apparatus for operating a differential microphone, the apparatus comprising a controller, configured to be coupled to the differential microphone and to:

(1) determine a distance between the differential microphone and a desired source of signal;

(2) compare the determined distance to a specified threshold distance;

(3) determine whether to operate the differential microphone in a nearfield mode of operation or a farfield mode of operation based on the comparison; and

(4) operate the differential microphone in the determined mode of operation.

42. A machine-readable medium, having encoded thereon program code, wherein, when the program code is executed by a machine, the machine implements a method for operating a differential microphone comprising the steps of:

(a) determining a distance between the differential microphone and a desired source of signal;

(b) comparing the determined distance to a specified threshold distance;

(c) determining whether to operate the differential microphone in a nearfield mode of operation or a farfield mode of operation based on the comparison of step (b); and

(d) operating the differential microphone in the determined mode of operation.