MIC COVERING DETECTION IN PERSONAL AUDIO DEVICES

• US 20120310640A1
• Filed: 09/30/2011
• Published: 12/06/2012
• Est. Priority Date: 06/03/2011
• Status: Active Grant

• Current Assignee: Cirrus Logic Incorporated
• Original Assignee: Cirrus Logic Incorporated
• Inventors: Kwatra, Nitin, Alderson, Jeffrey, Hendrix, Jon D.
• Granted Patent: US 8,958,571 B2
• Time in Patent Office: Days
• US Class Current: 704/233
• CPC Class Codes: G10K 11/175 using interference effects; Masking sound
• CPC Class Codes: G10K 11/17823 Reference signals, e.g. ambient acoustic environment
• CPC Class Codes: G10K 11/17825 Error signals
• CPC Class Codes: G10K 11/1783 handling or detecting of non-standard events or conditions, e.g. changing operating modes under specific operating conditions
• CPC Class Codes: G10K 11/17837 by retaining part of the ambient acoustic environment, e.g. speech or alarm signals that the user needs to hear
• CPC Class Codes: G10K 11/17854 the filter being an adaptive filter
• CPC Class Codes: G10K 11/17855 for improving speed or power requirements
• CPC Class Codes: G10K 11/17881 the reference signal being an acoustic signal, e.g. recorded with a microphone
• CPC Class Codes: G10K 11/17885 additionally using a desired external signal, e.g. pass-through audio such as music or speech
• CPC Class Codes: G10K 2210/108 Communication systems, e.g. where useful sound is kept and noise is cancelled
• CPC Class Codes: G10K 2210/30231 Sources, e.g. identifying noisy processes or components
• CPC Class Codes: G10K 2210/30391 Resetting of the filter parameters or changing the algorithm according to prevailing conditions
• CPC Class Codes: G10K 2210/503 Diagnostics; Stability; Alarms; Failsafe
• CPC Class Codes: G10L 21/0208 Noise filtering
• CPC Class Codes: H04M 1/20 Arrangements for preventing acoustic feed-back H04M1/62 takes precedence

Abstract

A personal audio device, such as a wireless telephone, includes noise canceling circuit that adaptively generates an anti-noise signal from a reference microphone signal and injects the anti-noise signal into the speaker or other transducer output to cause cancellation of ambient audio sounds. An error microphone may also be provided proximate the speaker to estimate an electro-acoustical path from the noise canceling circuit through the transducer. A processing circuit uses the reference and/or error microphone, optionally along with a microphone provided for capturing near-end speech, to determine whether one of the reference or error microphones is obstructed by comparing their received signal content and takes action to avoid generation of erroneous anti-noise.

Claims

1. A personal audio device, comprising:

a personal audio device housing;

a transducer mounted on the housing for reproducing an audio signal including both source audio for playback to a listener and an anti-noise signal for countering the effects of ambient audio sounds in the proximity of an acoustic output of the transducer;

a first microphone mounted on the housing that, when unobstructed, provides a first microphone signal indicative of the ambient audio sounds;

at least one second microphone mounted on the housing that, when unobstructed, provides at least one second microphone signal indicative of the ambient audio sounds; and

a processing circuit that implements an adaptive filter having a response that shapes the anti-noise signal, wherein the processing circuit further compares the first microphone signal and the at least one second microphone signal, and wherein the processing circuit, in response to determining that differences between the first microphone signal and the at least one second microphone signal indicate that the first microphone is at least partially obstructed, and takes action to prevent the anti-noise signal from being generated erroneously.

2. The personal audio device of claim 1, wherein the first microphone is a reference microphone that provides a reference microphone signal indicative of the ambient audio sounds, and wherein the processing circuit generates the anti-noise signal from the reference microphone signal.

3. The personal audio device of claim 2, wherein the at least one second microphone includes an error microphone that provides an error microphone signal indicative of the acoustic output of the transducer, wherein the processing circuit corrects the anti-noise signal for changes due to an electro-acoustic path through the transducer using the error microphone signal, and wherein the processing circuit determines the differences between the error microphone signal and the reference microphone signal.

4. The personal audio device of claim 3, wherein the at least one second microphone further includes a speech microphone provided for capturing near end speech of a user of the personal audio device and providing a speech signal indicative of the near end speech, and wherein the processing circuit takes the action in response to determining that differences between a first level of the ambient audio sounds present in the reference microphone signal, a second level of the ambient audio sounds present in the error microphone signal, and a third level of the ambient audio sounds present in the speech signal indicate that the reference microphone or the error microphone is at least partially obstructed.

5. The personal audio device of claim 1, wherein the first microphone is an error microphone that provides an error microphone signal indicative of the acoustic output of the transducer, wherein the processing circuit corrects the anti-noise signal for changes due to an electro-acoustic path through the transducer using the error microphone signal.

6. The personal audio device of claim 1, wherein the processing circuit takes action by muting the anti-noise signal.

7. The personal audio device of claim 1, wherein the processing circuit takes action by forcing the response of the adaptive filter to a known fixed response.

8. The personal audio device of claim 1, wherein the processing circuit detects the differences between the first microphone signal and the at least one second microphone signal only for frequencies below a cut-off frequency in order to determine that the error microphone is at least partially obstructed.

9. The personal audio device of claim 8, wherein the cutoff frequency is substantially equal to 100 Hz.

10. The personal audio device of claim 1, wherein the personal audio device is a wireless telephone further comprising a transceiver for receiving the source audio as a downlink audio signal.

11. The personal audio device of claim 1, wherein the personal audio device is an audio playback device, wherein the source audio is a program audio signal.

12. A method of preventing production of erroneous anti-noise a personal audio device having adaptive noise canceling, the method comprising:

producing an acoustic output with a transducer, the acoustic output including both source audio for playback to a listener and an anti-noise signal for countering the effects of ambient audio sounds in the proximity of an acoustic output of the transducer;

first measuring the ambient audio sounds with a first microphone;

second measuring the ambient audio sounds with at least one second microphone;

comparing the first microphone signal and the at least one second microphone signal to determine differences between the first microphone signal and the at least one second microphone signal;

determining whether the first microphone is at least partially obstructed from a result of the comparing; and

taking action in response to determining that the first microphone is at least partially obstructed to prevent the anti-noise signal from being generated erroneously.

13. The method of claim 12, wherein the first microphone is a reference microphone that provides a reference microphone signal indicative of the ambient audio sounds, and wherein the method further comprises generating the anti-noise signal from the reference microphone signal.

14. The method of claim 13, wherein the at least one second microphone includes an error microphone that provides an error microphone signal indicative of the acoustic output of the transducer, wherein the method further corrects the anti-noise signal for changes due to an electro-acoustic path through the transducer using the error microphone signal, and wherein the comparing compares the error microphone signal and the reference microphone signal.

15. The method of claim 14, wherein the at least one second microphone further includes a speech microphone provided for capturing near end speech of a user of the personal audio device and providing a speech signal indicative of the near end speech, and wherein the taking action is performed in response to determining that differences between a first level of the ambient audio sounds present in the reference microphone signal, a second level of the ambient audio sounds present in the error microphone signal, and a third level of the ambient audio sounds present in the speech signal indicate that the reference microphone or the error microphone is at least partially obstructed.

16. The method of claim 12, wherein the first microphone is an error microphone that provides an error microphone signal indicative of the acoustic output of the transducer, wherein the method further corrects the anti-noise signal for changes due to an electro-acoustic path through the transducer using the error microphone signal.

17. The method of claim 12, wherein the taking action mutes the anti-noise signal.

18. The method of claim 12, wherein the taking action forces the response of the adaptive filter to a known fixed response.

19. The method of claim 12, wherein the comparing detects the differences between the first microphone signal and the at least one second microphone signal only for frequencies below a cut-off frequency in order to determine that the first microphone is at least partially obstructed.

20. The method of claim 19, wherein the cutoff frequency is substantially equal to 100 Hz.

21. The method of claim 12, wherein the personal audio device is a wireless telephone, and wherein the method further comprises receiving the source audio as a downlink audio signal.

22. The method of claim 12, wherein the personal audio device is an audio playback device, wherein the source audio is a program audio signal.

23. An integrated circuit for implementing at least a portion of a personal audio device, comprising:

an output for providing a signal to a transducer including both source audio for playback to a listener and an anti-noise signal for countering the effects of ambient audio sounds in an acoustic output of the transducer;

a first microphone input for receiving a first microphone signal indicative of the ambient audio sounds from a first microphone;

at least one second microphone input for receiving a second microphone signal indicative of the ambient audio sounds from at least one second microphone; and

a processing circuit that implements an adaptive filter having a response that shapes the anti-noise signal, wherein the processing circuit further compares the first microphone signal and the at least one second microphone signal, and wherein the processing circuit, in response to determining that differences between the first microphone signal and the at least one second microphone signal indicate that the first microphone is at least partially obstructed, and takes action to prevent the anti-noise signal from being generated erroneously.

24. The integrated circuit of claim 23, wherein the first microphone signal is a reference microphone signal indicative of the ambient audio sounds, and wherein the processing circuit generates the anti-noise signal from the reference microphone signal.

25. The integrated circuit of claim 24, wherein the at least one second microphone signal includes an error microphone signal indicative of the acoustic output of the transducer, wherein the processing circuit corrects the anti-noise signal for changes due to an electro-acoustic path through the transducer using the error microphone signal, and wherein the processing circuit determines the differences between the error microphone signal and the reference microphone signal.

26. The integrated circuit of claim 25, wherein the at least one second microphone signal further includes a speech signal indicative of near end speech, and wherein the processing circuit takes the action in response to determining that differences between a first level of the ambient audio sounds present in the reference microphone signal, a second level of the ambient audio sounds present in the error microphone signal, and a third level of the ambient audio sounds present in the speech signal indicate that the first microphone or the at least one second microphone is at least partially obstructed.

27. The integrated circuit of claim 23, wherein the first microphone signal is an error microphone that provides an error microphone signal indicative of the acoustic output of the transducer, wherein the processing circuit corrects the anti-noise signal for changes due to an electro-acoustic path through the transducer using the error microphone signal.

28. The integrated circuit of claim 23, wherein the processing circuit takes action by muting the anti-noise signal.

29. The integrated circuit of claim 23, wherein the processing circuit takes action by forcing the response of the adaptive filter to a known fixed response.

30. The integrated circuit of claim 23, wherein the processing circuit detects the differences between the first microphone signal and the at least one second microphone signal only for frequencies below a cut-off frequency in order to determine that the first microphone is at least partially obstructed.

31. The integrated circuit of claim 30, wherein the cutoff frequency is substantially equal to 100 Hz.