Spatial interference suppression using dual-microphone arrays

• US 9,210,499 B2
• Filed: 12/13/2012
• Issued: 12/08/2015
• Est. Priority Date: 12/13/2012
• Status: Active Grant

• Current Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Original Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Inventors: Sun, Haohai, Moberg, Espen
• Primary Examiner(s): Holder, Regina N
• Application Number:
  US13/713,357
• Publication Number:
  US 20140169576A1
• Time in Patent Office: 1,090 Days
• Field of Search: None
• US Class Current: 1/1
• CPC Class Codes: H04R 1/326 for microphones H04R1/34 and H04R1/40 take precedence
• CPC Class Codes: H04R 1/406 microphones
• CPC Class Codes: H04R 2430/25 Array processing for suppression of unwanted side-lobes in directivity characteristics, e.g. a blocking matrix
• CPC Class Codes: H04R 3/005 for combining the signals of two or more microphones specially adapted for hearing aids H04R25/407

Abstract

Systems, processes, devices, apparatuses, algorithms and computer readable medium for suppressing spatial interference using a dual microphone array for receiving, from a first microphone and a second microphone that are separated by a predefined distance, and that are configured to receive source signals, respective first and second microphone signals based on received source signals. A phase difference between the first and the second microphone signals is calculated based on the predefined distance. An angular distance between directions of arrival of the source signals and a desired capture direction is calculated based on the phase difference. Directional-filter coefficients are calculated based on the angular distance. Undesired source signals are filtered from an output based on the directional-filter coefficients.

Claims

1. A device comprising:

a first microphone and a second microphone that are separated by a predefined distance, and that are configured to receive source signals and output respective first and second microphone signals based on received source signals; and

a signal processor configured to;

calculate a phase difference between the first and the second microphone signals based on the predefined distance, calculate an angular distance between directions of arrival of the source signals and a desired capture direction based on the phase difference; and

calculate directional-filter coefficients based on the angular distance, wherein

the signal processor is configured to filter undesired source signals from an output of the signal processor based on the directional-filter coefficients,

wherein the signal processor is configured to replace at least one of the directional-filter coefficients of a first range of subbands with an average value of the directional-filter coefficients for a second range of subbands.

2. The device according to claim 1, wherein the signal processor is configured to calculate phase differences, between the first and second microphone signals, for a particular short-time frame, across a plurality of discrete subbands of the first and second microphone signals.

3. The device according to claim 2, wherein the signal processor is configured to calculate angular distances, for a particular short-time frame, across a plurality of discrete subbands of the first and second microphone signals, by applying a trigonometric function to phase differences calculated by the signal processor.

4. The device according to claim 3, wherein the signal processor is configured to calculate direction-filter coefficients, for a particular short-time frame, across a plurality of discrete subbands of the first and second microphone signals, by applying a trigonometric function to angular distances calculated by the signal processor.

5. The device according to claim 1, wherein:

the first range of frequency subbands corresponds with 80˜

400 Hz, and

the second range of frequency subbands corresponds with 2˜

3 kHz.

6. The device according to claim 1, wherein the signal processor is configured to calculate a global gain using an average of robust subband directional-filter coefficients, and apply this average as the global to all the calculated subband directional-filter coefficients.

7. The device according to claim 6, wherein the robust subband directional-filter coefficients corresponds with 1˜

7 kHz.

8. The device according to claim 1, wherein the first and the second microphones are omnidirectional microphones, and the predefined distance is between 0.5 and 50 cm.

9. The device according to claim 8, wherein the predefined distance is about 2 cm.

10. The device according to claim 1, wherein:

the signal processor is configured to process the first and second microphone signals according to the following equations;

X₁(n,k)=S₁(n,k)·

exp(jφ

₁)+V₁(n,k), and

X₂(n,k)=S₂(n,k)·

exp(jφ

₂)+V₂(n,k), where

n denotes a short-time frame, k denotes a subband, and X_1,2, S_1,2, V_1,2, and φ

_1,2 denote, respectively, the microphone signals, signal amplitudes, noise, and phases of the first and second microphone signals; and

the signal processor is configured to calculate the phase difference according to the following equation;

Δ

φ

(n,k)=a tan 2{Im[X₁(n,k)],Re[X₁(n,k)]}−

a tan 2{Im[X₂(n,k)],Re[X₂(n,k)]}.

11. The device according to claim 10, wherein the signal processor is configured to calculate the angular difference according to the following equation:

12. The device according to claim 11, wherein the signal processor is configured to calculate the directional-filter coefficients according to the following equation:

G(n,k)={0.5+0.5·

cos[β

·

Δ

θ

(n,k)]}^α

, where

G(n,k) denotes the directional coefficient for frame n and subband k, β

is a parameter for beamwidth control, and α

is a suppression factor.

13. The device according to claim 12, wherein the signal processor is configured to improve low-frequency robustness of the calculate directional coefficients by:

replacing the directional-filter coefficients of a first range of subbands with an average value of the directional-filter coefficients for a second range of subbands, wherein the second range of subbands includes a range of frequencies that are higher than that of the first range of subbands.

14. The device according to claim 13, wherein the replacing is in accordance with the following equation:

G(n,k<sub>80˜

400 Hz</sub>)= G(n,k<sub>2˜

zkHz</sub>).

15. The device according to claim 14, wherein the signal processor is configured to reduce spatial aliasing by calculating a global gain using an average of robust subband directional-filter coefficients, and applying this average as the global to all the calculated subband directional-filter coefficients.

16. The device according to claim 15, wherein the robust subband directional-filter coefficients corresponds with 1˜

7 kHz.

17. One or more non-transitory computer readable storage mediums encoded with software comprising computer executable instructions, which when executed by one or more processors, execute a method comprising:

receiving, from a first microphone and a second microphone that are separated by a predefined distance, and that are configured to receive source signals, respective first and second microphone signals based on received source signals;

calculating a phase difference between the first and the second microphone signals based on the predefined distance;

calculating an angular distance between directions of arrival of the source signals and a desired capture direction based on the phase difference;

calculating directional-filter coefficients based on the angular distance;

replacing at least one of the directional-filter coefficients of a first range of subbands with directional-filter coefficients for a second range of subbands; and

filtering undesired source signals from an output based on the directional-filter coefficients.

18. A device comprising:

a first microphone and a second microphone that are separated by a predefined distance, and that are configured to receive source signals and output respective first and second microphone signals based on received source signals; and

a signal processor configured to;

calculate a phase difference between the first and the second microphone signals based on the predefined distance, calculate an angular distance between directions of arrival of the source signals and a desired capture direction based on the phase difference; and

calculate directional-filter coefficients based on the angular distance,

wherein the signal processor is configured to filter undesired source signals from an output of the signal processor based on the directional-filter coefficients,

wherein the signal processor is configured to replace each of the directional-filter coefficients of a first range of subbands with an average value of the directional-filter coefficients for a second range of subbands.