Frequency-shaped noise-based adaptation of secondary path adaptive response in noise-canceling personal audio devices

• US 9,319,784 B2
• Filed: 04/14/2014
• Issued: 04/19/2016
• Est. Priority Date: 04/14/2014
• Status: Active Grant

• Current Assignee: Cirrus Logic Incorporated
• Original Assignee: Cirrus Logic Incorporated
• Inventors: Lu, Yang, Zhou, Dayong, Li, Ning
• Primary Examiner(s): SING, SIMON P
• Application Number:
  US14/252,235
• Publication Number:
  US 20150296296A1
• Time in Patent Office: 736 Days
• US Class Current: 1/1
• 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 11/17854 the filter being an adaptive filter
• 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 2210/1081 Earphones, e.g. for telephones, ear protectors or headsets
• CPC Class Codes: G10K 2210/3028 Filtering, e.g. Kalman filters or special analogue or digital filters
• CPC Class Codes: G10K 2210/3049 Random noise used, e.g. in model identification
• CPC Class Codes: G10K 2210/3056 Variable gain
• CPC Class Codes: H04R 1/08 Mouthpieces; Microphones; Attachments therefor
• 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 2410/05 Noise reduction with a separate noise microphone
• CPC Class Codes: H04R 2460/01 Hearing devices using active noise cancellation
• 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

Abstract

A personal audio device 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 provide an error signal indicative of the effectiveness of the noise cancellation. A secondary path estimating adaptive filter is used to estimate the electro-acoustical path from the noise canceling circuit through the transducer so that source audio can be removed from the error signal. Noise is injected so that the adaptation of the secondary path estimating adaptive filter can be maintained, irrespective of the presence and amplitude of the source audio. The noise is shaped by a noise shaping filter that has a response controlled in conformity with at least one parameter of the secondary path response.

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 the ambient audio sounds at the transducer;

a controllable noise source for providing a noise signal; and

a processing circuit that filters the reference microphone signal with a first adaptive filter to generate the anti-noise signal to reduce the presence of the ambient audio sounds heard by the listener in conformity with an error signal and the reference microphone signal, wherein the processing circuit implements a noise shaping filter having a controllable frequency response that filters the noise signal to produce a frequency-shaped noise signal, wherein the processing circuit implements a secondary path adaptive 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 the error signal, and wherein the processing circuit injects the frequency-shaped noise signal into the secondary path adaptive filter and the audio signal reproduced by the transducer in place of or in combination with the source audio to cause the secondary path adaptive filter to continue to adapt when the source audio is absent or has reduced amplitude, and wherein the processing circuit controls the frequency response of the noise shaping filter in conformity with at least one parameter of the secondary path response to reduce audibility of the noise signal in the audio signal reproduced by the transducer.

2. The personal audio device of claim 1, wherein the processing circuit analyzes the error signal to determine frequency content of the error signal and adaptively controls the controllable frequency response of the noise shaping filter in conformity with the frequency content of the error signal.

3. The personal audio device of claim 2, wherein the controllable response of the noise shaping filter includes a response that is an inverse of at least a portion of the secondary path response, wherein the at least one parameter comprises parameters determinative of the secondary path response.

4. The personal audio device of claim 2, wherein a gain of the controllable frequency response of the noise shaping filter is set in conformity with an inverse of a magnitude of the secondary path response over at least a portion of the secondary path response.

5. The personal audio device of claim 1, wherein a gain of the controllable frequency response of the noise shaping filter is set in conformity with an inverse of a magnitude of the secondary path response in a particular frequency band.

6. The personal audio device of claim 1, wherein the processing circuit further frequency-smooths the controllable frequency response of the noise shaping to prevent generation of narrow peaks in a frequency spectrum of the frequency-shaped noise signal.

7. The personal audio device of claim 1, wherein the processing circuit further smooths the controllable frequency response of the noise shaping in the time domain to prevent abrupt changes in the amplitude of the frequency-shaped noise signal.

8. The personal audio device of claim 1, wherein the processing circuit further reduces a rate of update of the controllable frequency response of the noise shaping filter in response to an indication of system instability or an ambient audio condition that may cause improper generation of that anti-noise signal.

9. 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;

filtering the reference microphone signal with a first adaptive filter to generate an anti-noise signal to reduce the presence of the ambient audio sounds heard by the listener in conformity with an error signal and the reference microphone signal;

combining the anti-noise signal with source audio;

providing a result of the combining to a transducer;

measuring an acoustic output of the transducer and the ambient audio sounds with an error microphone;

shaping the source audio with a secondary path adaptive filter;

removing the source audio from the error microphone signal to provide the error signal;

generating a noise signal with a controllable noise source;

filtering the noise signal with a noise shaping filter having a controllable frequency response to produce a frequency-shaped noise signal;

injecting the frequency-shaped noise signal into the secondary path adaptive filter and the audio signal reproduced by the transducer in place of or in combination with the source audio to cause the secondary path adaptive filter to continue to adapt when the source audio is absent or has reduced amplitude; and

controlling the frequency response of the noise shaping filter in conformity with at least one parameter of the secondary path response to reduce audibility of the noise signal in the audio signal reproduced by the transducer.

10. The method of claim 9, further comprising analyzing the error signal to determine frequency content of the error signal and wherein the controlling adaptively controls the controllable frequency response of the noise shaping filter in conformity with the frequency content of the error signal.

11. The method of claim 10, wherein the controllable response of the noise shaping filter includes a response that is an inverse of at least a portion of the secondary path response, wherein the at least one parameter comprises parameters determinative of the secondary path response.

12. The method of claim 10, wherein the controlling sets a gain of the controllable frequency response of the noise shaping filter in conformity with an inverse of a magnitude of the secondary path response over at least a portion of the secondary path response.

13. The method of claim 9, wherein the controlling sets a gain of the controllable frequency response of the noise shaping filter in conformity with an inverse of a magnitude of the secondary path response in a particular frequency band.

14. The method of claim 9, wherein the controlling further comprises smoothing the controllable frequency response of the noise shaping to prevent generation of narrow peaks in a frequency spectrum of the frequency-shaped noise signal.

15. The method of claim 9, wherein the controlling further comprises smoothing the controllable frequency response of the noise shaping in the time domain to prevent abrupt changes in the amplitude of the frequency-shaped noise signal.

16. The method of claim 9, further comprising reducing a rate of update of the controllable frequency response of the noise shaping filter in response to an indication of system instability or an ambient audio condition that may cause improper generation of that anti-noise signal.

17. 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;

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

a controllable noise source for providing a noise signal; and

a processing circuit that filters the reference microphone signal with a first adaptive filter to generate the anti-noise signal to reduce the presence of the ambient audio sounds heard by the listener in conformity with an error signal and the reference microphone signal, wherein the processing circuit implements a noise shaping filter having a controllable frequency response that filters the noise signal to produce a frequency-shaped noise signal, wherein the processing circuit implements a secondary path adaptive 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 the error signal, and wherein the processing circuit injects the frequency-shaped noise signal into the secondary path adaptive filter and the audio signal reproduced by the transducer in place of or in combination with the source audio to cause the secondary path adaptive filter to continue to adapt when the source audio is absent or has reduced amplitude, and wherein the processing circuit controls the frequency response of the noise shaping filter in conformity with at least one parameter of the secondary path response to reduce audibility of the noise signal in the audio signal reproduced by the transducer.

18. The integrated circuit of claim 17, wherein the processing circuit analyzes the error signal to determine frequency content of the error signal and adaptively controls the controllable frequency response of the noise shaping filter in conformity with the frequency content of the error signal.

19. The integrated circuit of claim 18, wherein the controllable response of the noise shaping filter includes a response that is an inverse of at least a portion of the secondary path response, wherein the at least one parameter comprises parameters determinative of the secondary path response.

20. The integrated circuit of claim 18, wherein a gain of the controllable frequency response of the noise shaping filter is set in conformity with an inverse of a magnitude of the secondary path response over at least a portion of the secondary path response.

21. The integrated circuit of claim 17, wherein a gain of the controllable frequency response of the noise shaping filter is set in conformity with an inverse of a magnitude of the secondary path response in a particular frequency band.

22. The integrated circuit of claim 17, wherein the processing circuit further frequency-smooths the controllable frequency response of the noise shaping to prevent generation of narrow peaks in a frequency spectrum of the frequency-shaped noise signal.

23. The integrated circuit of claim 17, wherein the processing circuit further smooths the controllable frequency response of the noise shaping in the time domain to prevent abrupt changes in the amplitude of the frequency-shaped noise signal.

24. The integrated circuit of claim 17, wherein the processing circuit further reduces a rate of update of the controllable frequency response of the noise shaping filter in response to an indication of system instability or an ambient audio condition that may cause improper generation of that anti-noise signal.