Microphone partial occlusion detector

• US 9,467,779 B2
• Filed: 05/13/2014
• Issued: 10/11/2016
• Est. Priority Date: 05/13/2014
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: Myftari, Fatos, Iyengar, Vasu, Dusan, Sorin V., Lindahl, Aram M.
• Primary Examiner(s): HUBER, PAUL W
• Application Number:
  US14/276,988
• Publication Number:
  US 20150334489A1
• Time in Patent Office: 882 Days
• US Class Current: 1/1
• CPC Class Codes: H04R 1/08 Mouthpieces; Microphones; Attachments therefor
• CPC Class Codes: H04R 2499/11 Transducers incorporated or for use in hand-held devices, e.g. mobile phones, PDA's, camera's
• CPC Class Codes: H04R 3/002 Damping circuit arrangements for transducers, e.g. motional feedback circuits
• CPC Class Codes: H04R 3/005 for combining the signals of two or more microphones specially adapted for hearing aids H04R25/407
• CPC Class Codes: H04R 3/04 for correcting frequency response

Abstract

Digital signal processing for microphone partial occlusion detection is described. In one embodiment, an electronic system for audio noise processing and for noise reduction, using a plurality of microphones, includes a first noise estimator to process a first audio signal from a first one of the microphones, and generate a first noise estimate. The electronic system also includes a second noise estimator to process the first audio signal, and a second audio signal from a second one of the microphones, in parallel with the first noise estimator, and generate a second noise estimate. A microphone partial occlusion detector determines a low frequency band separation of the first and second audio signals and a high frequency band separation of the first and second audio signals to generate a microphone partial occlusion function that indicates whether one of the microphones is partially occluded.

Claims

1. An electronic system for audio noise processing and for noise reduction, using a plurality of microphones, comprising:

a first noise estimator to process a first audio signal from a first one of the microphones, and generate a first noise estimate;

a second noise estimator to process the first audio signal, and a second audio signal from a second one of the microphones, in parallel with the first noise estimator, and generate a second noise estimate;

a microphone partial occlusion detector to determine a low frequency band separation of the first and second audio signals and a high frequency band separation of the first and second audio signals, to generate a microphone partial occlusion function that indicates whether one of the microphones is partially occluded; and

a combiner-selector to receive the first and second noise estimates, and to generate an output noise estimate using the first and second noise estimates, wherein the combiner-selector is to generate its output noise estimate also based on the microphone partial occlusion function, wherein the combiner-selector selects the first noise estimate for its output noise estimate, and not the second noise estimate, when the microphone partial occlusion function indicates that the second one of the microphones is partially occluded.

2. The system of claim 1 wherein the microphone partial occlusion detector compares the high frequency band separation of the first and second audio signals and the low frequency band separation of the first and second audio signals.

3. The system of claim 2 wherein the microphone partial occlusion function takes on a value that indicates partial occlusion when a difference between the high frequency band separation of the first and second audio signals and the low frequency band separation of the first and second audio signals is greater than a threshold.

4. The system of claim 3 wherein the microphone partial occlusion function takes on another value that indicates no partial occlusion when the difference is less than the threshold.

5. The system of claim 3, wherein the first and second audio signals are converted from a time domain to a frequency domain to generate a measure of strength of the first audio signal and a measure of strength of the second audio signal.

6. The system of claim 5, wherein the low band frequency separation is computed with the following equation:

SEPlowband=1/M[summation of k=1 to M bins][10*log 10{[ps_first signal(k)}−

10*log 10{[ps_second signal(k)]}]

where M is a frequency bin closest to a frequency that depends upon a form factor of the electronic system and ps_first signal and ps_second signal are computed power levels for the first and second audio signals, respectively.

7. The system of claim 5, wherein the high band frequency separation is computed with the following equation:

SEPhighband=(1/(N−

M))[summation of k=M+1 to N bins][10*log 10{[ps_first signal (k)}−

10*log 10{[ps_second signal(k)]}]

where M is a frequency bin closest to a frequency that depends upon a form factor of the electronic system and ps_first signal and ps_second signal are computed power levels for the first and second audio signals, respectively.

8. A device having a microphone partial occlusion detector comprising:

means for processing first and second audio signals that are from first and second microphones, respectively, including means for determining a low frequency band separation of the first and second audio signals and a high frequency band separation of the first and second audio signals; and

means for evaluating a microphone partial occlusion function that indicates a likelihood of a second microphone being partially occluded, using the processed first and second audio signals wherein the processing means compares a high frequency band separation of the first and second audio signals and a low frequency band separation of the first and second audio signals wherein the microphone partial occlusion function takes on a value that indicates partial occlusion when a difference between the high frequency band separation of the first and second audio signals and the low frequency band separation of the first and second audio signals is greater than a threshold.

9. The device of claim 8 wherein the microphone partial occlusion function takes on another value that indicates no partial occlusion when the difference is less than the threshold.

10. The device of claim 8, wherein the first and second audio signals are converted from a time domain to a frequency domain to generate a measure of strength of the first audio signal and a measure of strength of the second audio signal.

11. The device of claim 10, wherein the low band frequency separation is computed with the following equation:

SEPlowband=1/M[summation of k=1 to M bins][10*log 10{[ps_first signal(k)}−

10*log 10{[ps_second signal(k)]}]

where M is a frequency bin closest to a frequency that depends upon a form factor of the device and ps_first signal and ps_second signal are computed power levels for the first and second audio signals, respectively.

12. The device of claim 10, wherein the high band frequency separation is computed with the following equation:

SEPhighband=(1/(N−

M))[summation of k=M+1 to N bins][10*log 10{[ps_first signal (k)}−

10*log 10{[ps_second signal(k)]}]

where M is a frequency bin closest to a frequency that depends upon a form factor of the device and ps_first signal and ps_second signal are computed power levels for the first and second audio signals, respectively.

13. A method for detecting partial occlusion of a microphone, comprising:

computing a microphone partial occlusion function for each input frame based on a low frequency band separation of first and second audio signals of first and second microphones respectively of a device and based on a high frequency band separation of the first and second audio signals; and

determining if the microphone partial occlusion function for each input frame is greater than a threshold using a partial occlusion algorithm; and

determining that a partial occlusion for one of the microphones has occurred if the microphone partial occlusion detection function is greater than the threshold.

14. The method of claim 13 further comprising:

determining that no partial occlusion for the microphones has occurred if the microphone partial occlusion function is less than the threshold.

15. The method of claim 13 wherein the first and second audio signals are converted from a time domain to a frequency domain to generate a measure of strength of the first audio signal and a measure of strength of the second audio signal.

16. The method of claim 13, wherein a full occlusion algorithm runs in parallel with the partial occlusion algorithm and when any type of full or partial occlusion is detected, a noise suppression algorithm switches from a two mic noise estimate to using a one mic noise estimate.

17. A method for detecting partial occlusion of a microphone, comprising:

computing a microphone partial occlusion function based on a low frequency band separation of first and second audio signals of first and second microphones respectively of a device and based on a high frequency band separation of the first and second audio signals;

determining if the microphone partial occlusion function is greater than a threshold and a partial occlusion condition of a microphone is currently not detected;

determining that a partial occlusion for one of the microphones of the device has occurred if the microphone partial occlusion detection function is greater than the threshold and the partial occlusion condition of a microphone is currently not detected.

18. The method of claim 17, further comprising:

determining if the microphone partial occlusion detection function is less than a threshold and a partial occlusion condition of a microphone is currently detected.

19. The method of claim 18, further comprising:

changing the partial occlusion condition of a microphone to being not detected if the microphone partial occlusion detection function is less than a threshold and the partial occlusion condition of the microphone is currently detected.

20. The method of claim 17 wherein the first and second audio signals are converted from a time domain to a frequency domain to generate a measure of strength of the first audio signal and a measure of strength of the second audio signal.