Hybrid adaptive noise cancellation system with filtered error microphone signal

• US 9,578,415 B1
• Filed: 08/21/2015
• Issued: 02/21/2017
• Est. Priority Date: 08/21/2015
• Status: Active Grant

• Current Assignee: Cirrus Logic Incorporated
• Original Assignee: Cirrus Logic Incorporated
• Inventors: Zhou, Dayong, Lu, Yang, Li, Ning, Kwatra, Nitin, Miller, Antonio J.
• Primary Examiner(s): Bernardi, Brenda
• Application Number:
  US14/832,585
• Publication Number:
  US 20170053638A1
• Time in Patent Office: 550 Days
• US Class Current: 1/1
• CPC Class Codes: G10K 11/16 Methods or devices for protecting against, or for damping, noise or other acoustic waves in general G10K11/36 takes precedence
• CPC Class Codes: G10K 11/17817 between the output signals and the error signals, i.e. secondary path
• 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 11/17853 of the filter
• CPC Class Codes: G10K 11/17854 the filter being an adaptive filter
• CPC Class Codes: G10K 11/17879 using both a reference signal and an error signal
• 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 2210/1082 Microphones, e.g. systems using "virtual" microphones
• CPC Class Codes: G10K 2210/3017 Copy, i.e. whereby an estimated transfer function in one functional block is copied to another block
• CPC Class Codes: G10K 2210/3022 Error paths
• CPC Class Codes: G10K 2210/3026 Feedback
• CPC Class Codes: G10K 2210/3027 Feedforward
• CPC Class Codes: G10K 2210/3035 Models, e.g. of the acoustic system
• CPC Class Codes: G10K 2210/3039 Nonlinear, e.g. clipping, numerical truncation, thresholding or variable input and output gain
• CPC Class Codes: G10K 2210/3045 Multiple acoustic inputs, single acoustic output
• CPC Class Codes: G10K 2210/3049 : Random noise used, e.g. in model identification
• CPC Class Codes: G10K 2210/3053 : Speeding up computation or convergence, or decreasing the computational load
• CPC Class Codes: G10K 2210/3055 : Transfer function of the acoustic system
• CPC Class Codes: G10K 2210/3056 : Variable gain
• CPC Class Codes: G10K 2210/509 : Hybrid, i.e. combining different technologies, e.g. passive and active
• 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 2499/11 : Transducers incorporated or for use in hand-held devices, e.g. mobile phones, PDA's, camera's
• 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

In accordance with systems and methods of the present disclosure, an adaptive noise cancellation system may include an alignment filter configured to correct misalignment of a reference microphone signal and an error microphone signal by generating a misalignment correction signal.

Claims

1. 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 a source audio signal for playback to a listener and an anti-noise signal for countering an effect 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 the ambient audio sounds at the transducer; and

a processing circuit that implements;

a feedforward filter having a response that generates at least a portion of the anti-noise signal from the reference microphone signal;

a secondary path estimate filter configured to model an electro-acoustic path of the source audio signal and have a response that generates a secondary path estimate from the source audio signal;

a feedback filter having a response that generates at least a portion of the anti-noise signal based on the error microphone signal;

an alignment filter configured to correct misalignment of the reference microphone signal and error microphone signal by generating a misalignment correction signal;

a feedforward coefficient control block that shapes the response of the feedforward filter by adapting the response of the feedforward filter to minimize the ambient audio sounds in the error microphone signal; and

a secondary path coefficient control block that shapes the response of the secondary path estimate filter in conformity with the source audio signal and the misalignment correction signal in order to minimize the misalignment correction signal.

2. The integrated circuit of claim 1, wherein the response of the feedback filter generates at least the portion of the anti-noise signal from a playback corrected error, the playback corrected error based on a difference between the error microphone signal and the secondary path estimate.

3. The integrated circuit of claim 2, wherein the misalignment correction signal comprises a filtered playback corrected error generated from the playback corrected error.

4. The integrated circuit of claim 3, wherein the feedforward control block shapes the response of the feedforward filter in conformity with the filtered playback corrected error and the reference microphone signal.

5. The integrated circuit of claim 1, wherein the alignment filter has a response given by 1+SE(z)H(z), where SE(z) is the response of the secondary path estimate filter and H(z) is the response of the feedback filter.

6. The integrated circuit of claim 1, wherein the processing circuit further implements a gain associated with the feedback filter.

7. The integrated circuit of claim 6, wherein the processing circuit further implements a secondary path estimate performance monitor for monitoring performance of the secondary path estimate filter in modeling the electro-acoustic path.

8. The integrated circuit of claim 7, wherein the processing circuit controls the gain responsive to the secondary path estimate performance monitor.

9. The integrated circuit of claim 8, wherein the alignment filter has a response given by 1+SE(z)H(z)G, where SE(z) is the response of the secondary path estimate filter, H(z) is the response of the feedback filter, and G is the gain.

10. The integrated circuit of claim 8, wherein the alignment filter has a response given by 1+SE_G(z)H(z)G, where SE_G(z) is a previously-stored response of the secondary path estimate filter existing at a time when, as determined by the secondary path estimate performance monitor, the secondary path estimate filter was sufficiently modeling the electro-acoustic path of the source audio signal, H(z) is the response of the feedback filter, and G is the gain.

11. The integrated circuit of claim 10, wherein the secondary path estimate performance monitor updates the stored response SE_G(z) at an update frequency dependent upon a degree of which the secondary path estimate filter is sufficiently modeling the electro-acoustic path of the source audio signal.

12. The integrated circuit of claim 10, wherein a filter having a response substantially equivalent to SE_G(z) is applied to the reference microphone signal to generate a filtered reference microphone signal communicated to the feedforward coefficient control block.

13. The integrated circuit of claim 1, wherein the secondary path coefficient control block shapes the response of the secondary path estimate filter by correlating the misalignment correction signal and a modified source audio signal in order to minimize the misalignment correction signal, wherein the modified source audio signal comprises the sum of the source audio signal and a portion of the anti-noise signal generated by the feedback filter.

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

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

receiving an error microphone signal indicative of the output of the transducer and the ambient audio sounds at the transducer;

generating a source audio signal for playback to a listener;

generating a feedforward anti-noise signal component from the reference microphone signal by adapting a response of an adaptive filter that filters the reference microphone signal to minimize the ambient audio sounds in the error microphone signal;

generating a feedback anti-noise signal component based on the error microphone signal, for countering the effects of ambient audio sounds at an acoustic output of the transducer;

generating a misalignment correction signal to correct misalignment of the reference microphone signal and error microphone signal;

generating the secondary path estimate from the source audio signal by adapting a response of a secondary path estimate filter that models an electro-acoustic path of the source audio signal and filters the source audio signal to minimize the filtered playback corrected error; and

combining the feedforward anti-noise signal component and the feedback anti-noise signal component with a source audio signal to generate an audio signal provided to the transducer.

15. The method of claim 14, wherein generating the feedback anti-noise signal component comprises filtering a playback corrected error with a feedback filter, the playback corrected error based on a difference between the error microphone signal and a secondary path estimate.

16. The method of claim 15, wherein generating the misalignment correction signal comprises generating a filtered playback corrected error from the playback corrected error.

17. The method of claim 16, wherein adapting the response of an adaptive filter that filters the reference microphone signal comprises shaping the response of the adaptive filter in conformity with the filtered playback corrected error and the reference microphone signal.

18. The method of claim 14, wherein the alignment filter has a response given by 1+SE(z)H(z), where SE(z) is the response of the secondary path estimate filter and H(z) is the response of the feedback filter.

19. The method of claim 14, further comprising applying a gain associated with the feedback filter.

20. The method of claim 19, further comprising monitoring with a secondary path estimate performance to monitor performance of the secondary path estimate filter in modeling the electro-acoustic path.

21. The method of claim 20, further comprising controlling a gain of the gain element responsive to the secondary path estimate performance monitor.

22. The method of claim 20, wherein the alignment filter has a response given by 1+SE(z)H(z)G, where SE(z) is the response of the secondary path estimate filter, H(z) is the response of the feedback filter, and G is the gain.

23. The method of claim 20, wherein the alignment filter has a response given by 1+SE_G(z)H(z)G, where SE_G(z) is a previously-stored response of the secondary path estimate filter existing at a time when, as determined by the secondary path estimate performance monitor, the secondary path estimate filter was sufficiently modeling the electro-acoustic path of the source audio signal, H(z) is the response of the feedback filter, and G is the gain.

24. The method of claim 23, further comprising updating the stored response SE_G(z) at an update frequency dependent upon a degree of which the secondary path estimate filter is sufficiently modeling the electro-acoustic path of the source audio signal.

25. The method of claim 23, further comprising applying a filter having a response substantially equivalent to SE_G(z) to the reference microphone signal to generate a filtered reference microphone signal communicated to the feedforward coefficient control block.

26. The method of claim 14, wherein the secondary path coefficient control block shapes the response of the secondary path estimate filter by correlating the misalignment correction signal and a modified source audio signal in order to minimize the misalignment correction signal, wherein the modified source audio signal comprises the sum of the source audio signal and a portion of the anti-noise signal generated by the feedback filter.

27. 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 a source audio signal for playback to a listener and an anti-noise signal for countering an effect 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 the ambient audio sounds at the transducer;

a noise input for receiving an injected, substantially inaudible noise signal; and

a processing circuit that implements;

a feedforward filter having a response that generates at least a portion of the anti-noise signal from the reference microphone signal;

a secondary path estimate filter configured to model an electro-acoustic path of the source audio signal and have a response that generates a secondary path estimate from the source audio signal;

a feedback filter having a response that generates at least a portion of the anti-noise signal based on the error microphone signal;

an effective secondary estimate filter configured to model an electro-acoustic path of the anti-noise signal and have a response that generates a filtered noise signal from the noise signal;

a feedforward coefficient control block that shapes the response of the feedforward filter in conformity with the error microphone signal and the reference microphone signal by adapting the response of the feedforward filter to minimize the ambient audio sounds in the error microphone signal;

a secondary path coefficient control block that shapes the response of the effective secondary path estimate filter in conformity with the noise signal and the error microphone signal in order to minimize the error signal; and

a secondary estimate construction block that generates the response of the secondary estimate filter from the response of the effective secondary estimate filter.

28. The integrated circuit of claim 27, wherein the secondary estimate construction block generates the response of the secondary estimate filter from the response of the effective secondary estimate filter in accordance with the equation:

29. The integrated circuit of claim 27, wherein the response of the feedback filter generates at least the portion of the anti-noise signal from a playback corrected error, the playback corrected error based on a difference between the error microphone signal and a sum of the secondary path estimate and a filtered noise signal.

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

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

receiving an error microphone signal indicative of an output of the transducer and the ambient audio sounds at the transducer;

generating a source audio signal for playback to a listener;

generating a feedforward anti-noise signal component from the reference microphone signal by adapting a response of an adaptive filter that filters the reference microphone signal to minimize the ambient audio sounds in the error microphone signal;

generating a feedback anti-noise signal component based on the error microphone signal;

generating the filtered noise signal from a noise signal by adapting a response of an effective secondary path estimate filter that models an electro-acoustic path of the anti-noise signal and filters the noise signal to minimize the error microphone signal;

generating the secondary path estimate from the source audio signal by applying a response of a secondary path estimate filter wherein the response of the secondary estimate filter is generated from the response of the effective secondary estimate filter; and

combining the feedforward anti-noise signal component and the feedback anti-noise signal component with a source audio signal to generate an audio signal provided to the transducer.

31. The method of claim 30, wherein a secondary estimate construction block generates the response of the secondary estimate filter from the response of the effective secondary estimate filter in accordance with the equation:

32. The method of claim 30, wherein generating the feedback anti-noise signal component comprises filtering a playback corrected error with a feedback filter, the playback corrected error based on a difference between the error microphone signal and a sum of a secondary path estimate and a filtered noise signal.