EAR-COUPLING DETECTION AND ADJUSTMENT OF ADAPTIVE RESPONSE IN NOISE-CANCELING IN PERSONAL AUDIO DEVICES

• US 20120207317A1
• Filed: 12/02/2011
• Published: 08/16/2012
• Est. Priority Date: 12/03/2010
• Status: Active Grant

• Current Assignee: Cirrus Logic Incorporated
• Original Assignee: Cirrus Logic Incorporated
• Inventors: Abdollahzadeh Milani, Ali, Kamath, Gautham Devendra
• Granted Patent: US 8,908,877 B2
• Time in Patent Office: Days
• US Class Current: 381/71.6
• CPC Class Codes: G10K 11/175 using interference effects; Masking sound
• CPC Class Codes: G10K 11/17817 between the output signals and the error signals, i.e. secondary path
• CPC Class Codes: G10K 11/17825 Error signals
• CPC Class Codes: G10K 11/17833 by using a self-diagnostic function or a malfunction prevention function, e.g. detecting abnormal output levels
• 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 2210/3039 Nonlinear, e.g. clipping, numerical truncation, thresholding or variable input and output gain
• CPC Class Codes: G10K 2210/3055 Transfer function of the acoustic system
• CPC Class Codes: G10K 2210/503 Diagnostics; Stability; Alarms; Failsafe

Abstract

A personal audio device, such as a wireless telephone, includes an adaptive noise canceling (ANC) 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 is also provided proximate the speaker to estimate an electro-acoustical path from the noise canceling circuit through the transducer. A processing circuit determines a degree of coupling between the user'"'"'s ear and the transducer and adjusts the adaptive cancellation of the ambient sounds to prevent erroneous and possibly disruptive generation of the anti-noise signal if the degree of coupling lies either below or above a range of normal operating ear contact pressure.

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 an acoustic output of the transducer;

a reference microphone mounted on the housing for providing a reference microphone signal indicative of the ambient audio sounds;

an error microphone mounted on the housing in proximity to the transducer for providing an error microphone signal indicative of the acoustic output of the transducer; and

a processing circuit that implements an adaptive filter having a response that shapes the anti-noise signal to reduce the presence of the ambient audio sounds heard by the listener, wherein the processing circuit determines a degree of coupling between the transducer and an ear of the listener and alters the response of the adaptive filter in conformity with the degree of coupling between the transducer and the ear of the listener.

2. The personal audio device of claim 1, wherein the processing circuit alters the response of the adaptive filter by forcing the response of the adaptive filter to a predetermined response in response to determining that the degree of coupling is greater than an upper threshold value.

3. The personal audio device of claim 2, wherein the predetermined response is a response that is trained to cancel the presence of the ambient audio sounds heard by the listener when the degree of coupling is greater than the upper threshold value.

4. The personal audio device of claim 2, wherein an adaptive control of the response of the adaptive filter has a leakage characteristic that restores the response of the adaptive filter to the predetermined response at an adjustable rate of change, and wherein the processing circuit increases the adjustable rate of change in response to determining the degree of coupling is greater than the upper threshold value.

5. The personal audio device of claim 1, wherein the processing circuit mutes the anti-noise signal in response to determining that the degree of coupling is lower than a lower threshold value.

6. The personal audio device of claim 5, wherein the processing circuit stops adaptation of the response of the adaptive filter in response to determining that the degree of coupling is lower than the lower threshold value.

7. The personal audio device of claim 5, wherein the processing circuit alters the response of the adaptive filter by forcing the response of the adaptive filter to a predetermined response in response to determining that the ear of the listener and the transducer to determining that the degree of coupling is greater than an upper threshold value.

8. The personal audio device of claim 7, wherein an adaptive control of the response of the adaptive filter has a leakage characteristic that restores the response of the adaptive filter to the predetermined response at an adjustable rate of change, and wherein the processing circuit increases the adjustable rate of change in response to determining that the degree of coupling is greater than the upper threshold value.

9. The personal audio device of claim 1, wherein the processing circuit implements a secondary path adaptive filter having a secondary path estimated response that shapes the source audio and a combiner that removes the source audio from the error microphone signal to provide an error signal indicative of the combined anti-noise and ambient audio sounds delivered to the listener, wherein the processing circuit adapts the response of the adaptive filter to minimize the error signal, and wherein the processing determines changes in the degree of coupling from changes in the secondary path estimated response.

10. The personal audio device of claim 9, wherein the processing circuit determines the degree of coupling between the transducer and the ear of the listener from a magnitude of the error signal weighted by an inverse of a peak magnitude of the secondary path response of the secondary path adaptive filter, wherein an decrease in the magnitude of the error signal weighted by the inverse of the peak magnitude of the secondary path response of the secondary path adaptive filter indicates a greater degree of coupling between the transducer and the ear of the listener.

11. The personal audio device of claim 9, wherein the processing circuit determines the degree of coupling between the transducer and the ear of the listener by comparing an indication of a peak magnitude of the secondary path response of the secondary path adaptive filter to a threshold value, wherein an increase in the peak magnitude of the secondary path response of the secondary path adaptive filter indicates a greater degree of coupling between the transducer and the ear of the listener.

12. A method of canceling ambient audio sounds in the proximity of a transducer of a personal audio device, the method comprising:

first measuring ambient audio sounds with a reference microphone;

second measuring an output of the transducer with an error microphone;

adaptively generating an anti-noise signal from a result of the first measuring for countering the effects of ambient audio sounds at an acoustic output of the transducer by adapting a response of an adaptive filter that filters an output of the reference microphone;

combining the anti-noise signal with a source audio signal to generate an audio signal provided to the transducer;

determining a degree of coupling between the transducer and an ear of the listener;

altering the response of the adaptive filter in conformity with the degree of coupling between the transducer and the ear of the listener;

combining the anti-noise signal with a source audio signal; and

providing a result of the combining to the transducer to generate the acoustic output.

13. The method of claim 12, wherein the altering alters the response of the adaptive filter by forcing the response of the adaptive filter to a predetermined response in response to determining that the degree of coupling is greater than an upper threshold.

14. The method of claim 13, wherein the predetermined response is a response that is trained to cancel the presence of the ambient audio sounds heard by the listener in response to determining that the degree of coupling is greater than an upper threshold.

15. The method of claim 13, wherein an adaptive control of the response of the adaptive filter has a leakage characteristic that restores the response of the adaptive filter to a predetermined response at an adjustable rate of change, and wherein the altering increases the adjustable rate of change in response to determining that the degree of coupling is less than a lower threshold.

16. The method of claim 12, further comprising muting the anti-noise signal in response to determining that the degree of coupling is less than a lower threshold.

17. The method of claim 16, wherein the altering stops adaptation of the response of the adaptive filter in response to determining that the degree of coupling is less than the lower threshold.

18. The method of claim 16, wherein the altering alters the response of the adaptive filter by forcing the response of the adaptive filter to a predetermined response in response to determining that the degree of coupling is greater than an upper threshold.

19. The method of claim 18, wherein an adaptive control of the response of the adaptive filter has a leakage characteristic that restores the response of the adaptive filter to a predetermined response at an adjustable rate of change, and wherein the altering increases the adjustable rate of change in response to determining the degree of coupling is less than the lower threshold.

20. The method of claim 12, further comprising:

shaping the source audio using a secondary path adaptive filter having a secondary path estimated response; and

removing the source audio from the error microphone signal to provide an error signal indicative of the combined anti-noise and ambient audio sounds delivered to the listener, wherein the adaptively generating adapts the response of the adaptive filter to minimize the error signal, and wherein the determining determines changes in the degree of coupling from changes in the secondary path estimated response.

21. The method of claim 20, wherein the determining determines the degree of coupling between the transducer and the ear of the listener from a magnitude of the error signal weighted by an inverse of a peak magnitude of the secondary path response of the secondary path adaptive filter, wherein a decrease in the magnitude of the error signal weighted by the inverse of the peak magnitude of the secondary path response of the secondary path adaptive filter indicates a greater degree of coupling between the transducer and the ear of the listener.

22. The method of claim 20, wherein the determining determines the degree of coupling between the transducer and the ear of the listener from an indication of a peak magnitude of the secondary path response of the secondary path adaptive filter wherein an increase in the peak magnitude of the secondary path response of the secondary path adaptive filter indicates a greater degree of coupling between the transducer and the ear of the listener.

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

an error microphone input for receiving an error microphone signal indicative of the output of the transducer; and

a processing circuit that implements an adaptive filter having a response that shapes the anti-noise signal to reduce the presence of the ambient audio sounds heard by the listener, wherein the processing circuit determines a degree of coupling between the transducer and an ear of the listener and alters the response of the adaptive filter in conformity with the degree of coupling between the transducer and the ear of the listener.

24. The integrated circuit of claim 23, wherein the processing circuit alters the response of the adaptive filter by forcing the response of the adaptive filter to a predetermined response in response to determining that the degree of coupling is greater than an upper threshold.

25. The integrated circuit of claim 24, wherein the predetermined response is a response that is trained to cancel the presence of the ambient audio sounds heard by the listener in response to determining that the degree of coupling is greater than the upper threshold.

26. The integrated circuit of claim 24, wherein an adaptive control of the response of the adaptive filter has a leakage characteristic that restores the response of the adaptive filter to a predetermined response at an adjustable rate of change, and wherein the processing circuit increases the adjustable rate of change in response to determining that the degree of coupling is greater than the upper threshold.

27. The integrated circuit of claim 26, wherein the processing circuit mutes the anti-noise signal in response to determining that when the degree of coupling is less than a lower threshold.

28. The integrated circuit of claim 27, wherein the processing circuit stops adaptation of the response of the adaptive filter in response to determining that the degree of coupling is less than the lower threshold.

29. The integrated circuit of claim 27, wherein the processing circuit alters the response of the adaptive filter by forcing the response of the adaptive filter to a predetermined response in response to determining that the degree of coupling is greater than an upper threshold.

30. The integrated circuit of claim 29, wherein an adaptive control of the response of the adaptive filter has a leakage characteristic that restores the response of the adaptive filter to the predetermined response at an adjustable rate of change, and wherein the processing circuit increases the adjustable rate of change in response to determining that the degree of coupling is greater than the upper threshold.

31. The integrated circuit of claim 23, wherein the processing circuit implements a secondary path adaptive filter having a secondary path estimated response that shapes the source audio and a combiner that removes the source audio from the error microphone signal to provide an error signal indicative of the combined anti-noise and ambient audio sounds delivered to the listener, wherein the processing circuit adapts the response of the adaptive filter to minimize the error signal, and wherein the processing determines changes in the degree of coupling from changes in the secondary path estimated response.

32. The personal audio device of claim 31, wherein the processing circuit determines the degree of coupling between the transducer and the ear of the listener from a magnitude of the error signal weighted by an inverse of a peak magnitude of the secondary path response of the secondary path adaptive filter, wherein an decrease in the magnitude of the error signal weighted by the inverse of the peak magnitude of the secondary path response of the secondary path adaptive filter indicates a greater degree of coupling between the transducer and the ear of the listener.

33. The integrated circuit of claim 31, wherein the processing circuit determines the degree of coupling between the transducer and the ear of the listener by comparing an indication of a peak magnitude of the secondary path response of the secondary path adaptive filter to a threshold value, wherein an increase in the peak magnitude of the secondary path response of the secondary path adaptive filter indicates a greater degree of coupling between the transducer and the ear of the listener.