MIC COVERING DETECTION IN PERSONAL AUDIO DEVICES

• US 20150104032A1
• Filed: 12/22/2014
• Published: 04/16/2015
• 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 10,468,048 B2
• Time in Patent Office: Days
• US Class Current: 381/71.11
• 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 plurality of microphones, including a first microphone mounted on the housing that, when unobstructed, provides a first microphone signal indicative of the ambient audio sounds, wherein a second microphone of the plurality of microphones is mounted on the housing and that, when unobstructed, provides a second microphone signal indicative of the ambient audio sounds; and

a processing circuit that implements a first adaptive filter having a response that generates the anti-noise signal from the first microphone signal, a second adaptive filter for generating shaped source audio from the source audio and a combiner for removing the shaped source audio from the second microphone signal to generate an error signal provided to a coefficient control block that controls coefficients of the first adaptive filter, wherein the processing circuit implements a first signal level detector for detecting a first amplitude of a given one of the first microphone signal or the second microphone signal to generate a microphone level signal and a second signal level detector for detecting a second amplitude of one of the plurality of microphones other than the given microphone to generate a reference level signal, wherein the processing circuit compares the microphone level signal and the reference level signal, in response to determining that differences between the microphone level signal and the reference level signal indicate that the first microphone is at least partially obstructed, halts or resets adaptation of a given one of at least one of the first adaptive filter or the second adaptive filter to prevent the anti-noise signal from being generated erroneously.

2. The personal audio device of claim 1, wherein the first signal level detector detects a level of the reference microphone signal.

3. The personal audio device of claim 2, wherein the second microphone is an error microphone that provides an error microphone signal indicative of the acoustic output of the transducer, wherein the second signal level detector detects the second amplitude of the error microphone signal.

4. The personal audio device of claim 3, wherein the plurality of microphones 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 halts the adaptation of the given adaptive filter in response to determining that differences between the microphone level signal, the reference level signal, and another reference level generated by detecting an amplitude of 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 processing circuit further, in response to determining that the differences between the microphone level signal and the reference level signal indicate that the first microphone is at least partially obstructed, mutes the anti-noise signal.

6. The personal audio device of claim 1, wherein the processing circuit further filters the first microphone signal and the second microphone signal to retain only frequencies below a cut-off frequency at inputs to the first signal level detector and the second signal level detector in order to determine that the given microphone is at least partially obstructed.

7. The personal audio device of claim 6, wherein the cutoff frequency is substantially equal to 100 Hz.

8. A method of preventing production of erroneous anti-noise in 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 of a plurality of microphones to generate a first microphone signal;

generating the anti-noise signal from the first microphone signal with a first adaptive filter;

second measuring the ambient audio sounds with second microphone of the plurality of microphones to generate a second microphone signal;

first detecting a first amplitude of a given one of the first microphone signal or the second microphone signal to generate a microphone level signal;

second detecting a second amplitude of one of the plurality of microphones other than the given microphone signal to generate a reference level signal;

comparing the microphone level signal and a signal level of one of the plurality of microphones other than the first microphone to determine differences between the microphone level signal and the reference level signal;

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

in response to determining that the first microphone is at least partially obstructed, halting or resetting adaptation of a given one of at least one of the first adaptive filter or the second adaptive filter to prevent the anti-noise signal from being generated erroneously.

9. The method of claim 8, wherein the first detecting detects a level of the reference microphone signal.

10. The method of claim 9, wherein the second microphone is an error microphone that provides an error microphone signal indicative of the acoustic output of the transducer, wherein the second detecting detects the second amplitude of the error microphone signal.

11. The method of claim 10, wherein the plurality of microphones 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, wherein the comparing determines that differences between the microphone level signal, the reference level signal, and another reference level generated by detecting an amplitude of the speech signal indicate that the reference microphone or the error microphone is at least partially obstructed, and wherein in response to determining that the reference microphone or the error microphone is at least partially obstructed, the halting or resetting halts or resets adaptation of the given adaptive filter.

12. The method of claim 8, further comprising muting the anti-noise signal in response to determining that the differences between the microphone level signal and the reference level signal indicate that the first microphone is at least partially obstructed.

13. The method of claim 8, wherein the comparing detects the differences between the first microphone signal and the second microphone signal only for frequencies below a cut-off frequency in order to determine that the first microphone is at least partially obstructed.

14. 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 of a plurality of microphone inputs for receiving a first microphone signal indicative of the ambient audio sounds from a first microphone;

a second microphone input of the plurality of microphone inputs for receiving a second microphone signal indicative of the ambient audio sounds from a second microphone; and

a plurality of microphones, including a first microphone mounted on the housing that, when unobstructed, provides a first microphone signal indicative of the ambient audio sounds, wherein a second microphone of the plurality of microphones is mounted on the housing and that, when unobstructed, provides a second microphone signal indicative of the ambient audio sounds; and

a processing circuit that implements a first adaptive filter having a response that generates the anti-noise signal from the first microphone signal, a second adaptive filter for generating shaped source audio from the source audio and a combiner for removing the shaped source audio from the second microphone signal to generate an error signal provided to a coefficient control block that controls coefficients of the first adaptive filter, wherein the processing circuit implements a first signal level detector for detecting a first amplitude of a given one of the first microphone signal or the second microphone signal to generate a microphone level signal and second signal level detector for detecting a second amplitude of the plurality of microphones other than the given microphone to generate a reference level signal, wherein the processing circuit compares the microphone level signal and the reference level signal, in response to determining that differences between the microphone level signal and the reference level signal indicate that the first microphone is at least partially obstructed, halts or resets adaptation of a given one of at least one of the first adaptive filter to prevent the anti-noise signal from being generated erroneously.

15. The integrated circuit of claim 14, wherein the first signal level detector detects a level of the reference microphone signal.

16. The integrated circuit of claim 15, wherein the second microphone signal is an error microphone signal indicative of the acoustic output of the transducer, wherein the second signal level detector detects the second amplitude of the error microphone signal.

17. The integrated circuit of claim 16, wherein the plurality of microphone inputs includes a speech microphone input for receiving a speech signal indicative of near end speech, and wherein the processing circuit halts or resets the adaptation of the given adaptive filter in response to determining that differences between the microphone level signal, the reference level signal, and another reference level generated by detecting an amplitude of the speech signal indicate that the first microphone or the second microphone is at least partially obstructed.

18. The integrated circuit of claim 14, wherein the processing circuit further, in response to determining that the differences between the microphone level signal and the reference level signal indicate that the first microphone is at least partially obstructed, mutes the anti-noise signal.

19. The integrated circuit of claim 14, wherein the processing circuit further filters the first microphone signal and the second microphone signal to retain only frequencies below a cut-off frequency at inputs to the first signal level detector and the second signal level detector in order to determine that the first microphone is at least partially obstructed.

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