Frequency and direction-dependent ambient sound handling in personal audio devices having adaptive noise cancellation (ANC)

• US 9,319,781 B2
• Filed: 03/04/2013
• Issued: 04/19/2016
• Est. Priority Date: 05/10/2012
• Status: Active Grant

• Current Assignee: Cirrus Logic Incorporated
• Original Assignee: Cirrus Logic Incorporated
• Inventors: Alderson, Jeffrey, Hendrix, Jon D., Zhou, Dayong
• Primary Examiner(s): Kim, Paul S
• Assistant Examiner(s): Faley, Katherine
• Application Number:
  US13/784,018
• Publication Number:
  US 20130301846A1
• Time in Patent Office: 1,142 Days
• Field of Search: 381/71.1, 381/71.2, 381/71.3, 381/71.4, 381/71.5, 381/71.6, 381/71.7, 381/71.8, 381/71.9, 381/71.11, 381/71.12, 381/71.13, 381/71.14
• US Class Current: 1/1
• CPC Class Codes: G10K 11/178 by electro-acoustically regenerating the original acoustic waves in anti-phase
• CPC Class Codes: G10K 11/17817 between the output signals and the error signals, i.e. secondary path
• CPC Class Codes: G10K 11/17819 between the output signals and the reference signals, e.g. to prevent howling
• 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 11/17827 Desired external signals, e.g. pass-through audio such as music or speech
• CPC Class Codes: G10K 11/17854 the filter being an adaptive filter
• CPC Class Codes: G10K 11/17857 Geometric disposition, e.g. placement of microphones
• 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 2210/3012 Algorithms
• CPC Class Codes: G10K 2210/30231 Sources, e.g. identifying noisy processes or components
• CPC Class Codes: G10K 2210/3025 Determination of spectrum characteristics, e.g. FFT
• CPC Class Codes: G10K 2210/3028 Filtering, e.g. Kalman filters or special analogue or digital filters
• CPC Class Codes: G10K 2210/30391 Resetting of the filter parameters or changing the algorithm according to prevailing conditions
• CPC Class Codes: G10K 2210/3226 Sensor details, e.g. for producing a reference or error signal
• CPC Class Codes: G10K 2210/503 Diagnostics; Stability; Alarms; Failsafe
• CPC Class Codes: H04R 1/1083 Reduction of ambient noise active noise reduction per se G10K11/175; protective devices for the ear, e.g. providing acoustic protection A61F11/06
• CPC Class Codes: H04R 3/00 Circuits for transducers , loudspeakers or microphones
• CPC Class Codes: H04R 3/002 : Damping circuit arrangements for transducers, e.g. motional feedback circuits

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 measure the output of the transducer in order to control the adaptation of the anti-noise signal and to estimate an electro-acoustical path from the noise canceling circuit through the transducer. A processing circuit that performs the adaptive noise canceling (ANC) function also detects frequency-dependent characteristics in and/or direction of the ambient sounds and alters adaptation of the noise canceling circuit in response to the detection.

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 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 the ambient audio sounds at the transducer; and

a processing circuit that generates the anti-noise signal from the reference microphone signal to reduce the presence of the ambient audio sounds heard by the listener using an adaptive filter having a response controlled by a coefficient control block having a first input receiving a first signal derived from the reference microphone signal and a second input receiving a second signal derived from the error microphone signal, wherein the processing circuit analyzes the reference microphone signal to detect ambient sounds and determine one or more frequencies or frequency bands in which the ambient sounds have energy, and wherein the processing circuit alters adaptation of the response of the adaptive filter in response to the detection of the ambient sounds and in conformity with a result of determining the one or more frequencies or frequency bands by altering frequency content of either the first signal or the second signal to reduce a sensitivity of the adaptation of the response of the adaptive filter at the one or more frequencies or frequency bands.

2. The personal audio device of claim 1, wherein the processing circuit further implements a secondary path filter having a secondary path 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, and wherein the second input of the coefficient control block receives the error signal as the second signal, whereby the response of the adaptive filter is controlled in conformity with the error signal and the reference microphone signal.

3. The personal audio device of claim 2, wherein the processing circuit filters at least one of the first or second signals with a non-adaptive filter having a fixed response selected in conformity with the one or more frequencies or frequency bands, so that sensitivity of the adaptation of the response of the adaptive filter is reduced at the one or more frequencies or frequency bands by the fixed response.

4. The personal audio device of claim 3, wherein the processing circuit selects the fixed response from among multiple predetermined frequency responses.

5. The personal audio device of claim 1, wherein the processing circuit detects the ambient sounds in both of the reference microphone signal and the error microphone signal.

6. The personal audio device of claim 5, wherein the processing circuit determines a direction of the ambient sounds, and wherein the processing circuit alters the adaptation of the response of the adaptive filter selectively in conformity with the direction of the ambient sounds.

7. The personal audio device of claim 1, further comprising a near-speech microphone mounted on the housing for providing a near-speech microphone signal indicative of speech of the listener and the ambient sounds, wherein the processing circuit further detects the ambient sounds in the near-speech microphone signal.

8. The personal audio device of claim 1, wherein the processing circuit detects the ambient sounds by measuring an amplitude of the reference microphone signal in the one or more frequencies or frequency bands.

9. The personal audio device of claim 8, wherein the one or more frequencies or frequency bands are selectable.

10. The personal audio device of claim 8, further comprising:

a headset connector for connecting an external headset; and

a headset type detection circuit for detecting a type of the external headset, and wherein the processing circuit further determines the one or more frequencies or frequency bands in conformity with the detected type of the external headset.

11. The personal audio device of claim 1, wherein the detecting detects whether low-frequency content is present.

12. The personal audio device of claim 1, wherein the detecting detects whether high-frequency content is present.

13. The personal audio device of claim 1, wherein the altering alters a rate of update of a coefficient control block of the adaptive filter.

14. The personal audio device of claim 1, wherein the processing circuit controls a variable portion of a frequency response of the adaptive filter with a leakage characteristic that restores the response of the adaptive filter to a predetermined response at a particular rate of change, and wherein the processing circuit alters the particular rate of change in conformity with a result of the detection of the ambient sounds.

15. The personal audio device of claim 1, wherein the processing circuit alters the frequency content of either the first signal or the second signal by injecting a signal having frequency content that reduces the sensitivity of the response of the adaptive filter at the one or more frequencies or frequency bands.

16. A method of countering effects of ambient audio sounds by a personal audio device, the method comprising:

measuring the ambient audio sounds with a reference microphone to generate a reference microphone signal;

measuring an acoustic output of a transducer and the ambient audio sounds with an error microphone to generate an error microphone signal;

adaptively generating an anti-noise signal from the reference microphone signal to reduce the presence of the ambient audio sounds heard by the listener using an adaptive filter having a response controlled by coefficients computed by a coefficient control block having a first input receiving a first signal derived from the reference microphone signal and a second input receiving a second signal derived from the error microphone signal;

combining the anti-noise signal with source audio;

providing a result of the combining to the transducer;

analyzing the reference microphone signal to detect ambient sounds and determine one or more frequencies or frequency bands in which the ambient sounds have energy; and

altering adaptation of the response of the adaptive filter in response to the detection of the ambient sounds and in conformity with a result of determining the one or more frequencies or frequency bands by altering frequency content of either the first signal or the second signal to reduce a sensitivity of adaptation of the response of the adaptive filter to the detected ambient sounds.

17. The method of claim 16, wherein the adaptively generating further generates the anti-noise signal from an error signal indicative of the acoustic output of the transducer and the ambient sounds, wherein the method further comprises:

shaping the source audio with a secondary path response provided by a secondary path adaptive filter; and

removing the shaped source audio from the error microphone signal to generate the error signal.

18. The method of claim 17, wherein the altering frequency content comprises filtering the first signal or the second signal with a non-adaptive filter having a fixed response selected in conformity with the one or more frequencies or frequency bands, so that sensitivity of the adaptation of the response of the adaptive filter is reduced at the one or more frequencies or frequency bands by the fixed response.

19. The method of claim 18, further comprising selecting the fixed response from among multiple predetermined frequency responses.

20. The method of claim 16, wherein the detecting detects the ambient sounds in both of the reference microphone signal and the error microphone signal.

21. The method of claim 20, wherein the method further comprises determining a direction of the ambient sounds, and wherein the altering alters the adaptation of the response of the adaptive filter selectively in conformity with the determined direction of the ambient sounds.

22. The method of claim 16, wherein the personal audio device includes a near-speech microphone mounted on a housing of the personal audio device for providing a near-speech microphone signal indicative of speech of the listener and the ambient sounds, and wherein the detecting further detects the ambient sounds in the near-speech microphone signal.

23. The method of claim 16, wherein the detecting detects the ambient sounds by measuring an amplitude of the reference microphone signal in the one or more frequencies or frequency bands.

24. The method of claim 23, further comprising selecting the one or more frequencies or frequency bands from among multiple predetermined frequencies or frequency bands.

25. The method of claim 23, further comprising:

connecting an external headset to the personal audio device; and

detecting a type of the external headset, and wherein the determining further determines the one or more frequencies or frequency bands in conformity with the detected type of the external headset.

26. The method of claim 16, wherein the detecting detects whether low-frequency content is present.

27. The method of claim 16, wherein the detecting detects whether high-frequency content is present.

28. The method of claim 16, wherein the altering alters a rate of update of a coefficient control block of the adaptive filter.

29. The method of claim 16, further comprising:

controlling a variable portion of a frequency response of the adaptive filter with a leakage characteristic that restores the response of the adaptive filter to a predetermined response at a particular rate of change; and

altering the particular rate of change in conformity with a result of the detection of the ambient sounds.

30. The method of claim 16, wherein the altering alters the frequency content of the first signal or the second signal by injecting a signal having frequency content that reduces the sensitivity of the response of the adaptive filter at the one or more frequencies or frequency bands.

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

an output for providing an output signal to an output 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;

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 acoustic output of the transducer and the ambient audio sounds at the transducer; and

a processing circuit that generates the anti-noise signal from the reference microphone signal to reduce the presence of the ambient audio sounds heard by the listener using an adaptive filter having a response controlled by a coefficient control block having a first input receiving a first signal derived from the reference microphone signal and a second input receiving a second signal derived from the error microphone signal, wherein the processing circuit analyzes the reference microphone signal to detect ambient sounds and determine one or more frequencies or frequency bands in which the ambient sounds have energy, and wherein the processing circuit alters adaptation of the response of the adaptive filter in response to the detection of the ambient sounds and in conformity with a result of determining the one or more frequencies or frequency bands by altering frequency content of either the first signal or the second signal to reduce a sensitivity of the adaptation of the response of the adaptive filter at the one or more frequencies or frequency bands.

32. The integrated circuit of claim 31, wherein the processing circuit further implements a secondary path filter having a secondary path 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, and wherein the second input of the coefficient control block receives the error signal as the second signal, whereby the response of the adaptive filter is controlled in conformity with the error signal and the reference microphone signal.

33. The integrated circuit of claim 32 wherein the processing circuit filters at least one of the first or second signals with a non-adaptive filter having a fixed response selected in conformity with the one or more frequencies or frequency bands, so that sensitivity of the adaptation of the response of the adaptive filter is reduced at the one or more frequencies or frequency bands by the fixed response.

34. The integrated circuit of claim 33, wherein the processing circuit selects the fixed response from among multiple predetermined frequency responses.

35. The integrated circuit of claim 31, wherein the processing circuit detects the ambient sounds in both of the reference microphone signal and the error microphone signal.

36. The integrated circuit of claim 35, wherein the processing circuit determines a direction of the ambient sounds, and wherein the processing circuit alters the adaptation of the adaptive filter selectively in conformity with the direction of the ambient sounds.

37. The integrated circuit of claim 31, further comprising a near speech microphone input for receiving a near-speech microphone signal indicative of speech of the listener and the ambient sounds, wherein the processing circuit detects the ambient sounds in the near-speech microphone signal.

38. The integrated circuit of claim 31, wherein the processing circuit detects the ambient sounds by measuring an amplitude of the reference microphone signal in the one or more frequencies or frequency bands.

39. The integrated circuit of claim 38, wherein the one or more frequencies or frequency bands are selectable.

40. The integrated circuit of claim 38, further comprising a headset type detection circuit for detecting a type of an external headset coupled to the output, and wherein the processing circuit further determines the one or more frequencies or frequency bands in conformity with the detected type of the external headset.

41. The integrated circuit of claim 31, wherein the detecting detects whether low-frequency content is present.

42. The integrated circuit of claim 31, wherein the detecting detects whether high-frequency content is present.

43. The integrated circuit of claim 31, wherein the altering alters a rate of update of a coefficient control block of the adaptive filter.

44. The integrated circuit of claim 31, wherein the processing circuit controls a variable portion of a frequency response of the adaptive filter with a leakage characteristic that restores the response of the adaptive filter to a predetermined response at a particular rate of change, and wherein the processing circuit alters the particular rate of change in conformity with a result of the detection of the ambient sounds.

45. The integrated circuit of claim 31, wherein the processing circuit alters the frequency content of either the first signal or the second signal by injecting a signal having frequency content that reduces the sensitivity of the response of the adaptive filter at the one or more frequencies or frequency bands.