Bandlimiting anti-noise in personal audio devices having adaptive noise cancellation (ANC)

• US 9,824,677 B2
• Filed: 05/16/2012
• Issued: 11/21/2017
• Est. Priority Date: 06/03/2011
• Status: Active Grant

• Current Assignee: Cirrus Logic Incorporated
• Original Assignee: Cirrus Logic Incorporated
• Inventors: Kwatra, Nitin, Abdollahzadeh Milani, Ali, Alderson, Jeffrey
• Primary Examiner(s): Goins, Davetta W
• Assistant Examiner(s): GANMAVO, KUASSI A
• Application Number:
  US13/472,755
• Publication Number:
  US 20120308028A1
• Time in Patent Office: 2,015 Days
• Field of Search: 381338, 381337, 381 72, 381 711, 381 716, 381 91, 381 92, 381 941- 943, 381 947- 948, 381 945, 381123, 381104, 381107, 704200, 704225, 37940601-40606, 37938701, 37939201, 379395
• 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 11/17854 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 2210/3012 Algorithms
• 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 2210/30231 Sources, e.g. identifying noisy processes or components
• 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 2210/507 Flow or turbulence
• CPC Class Codes: G10K 2210/508 Reviews on ANC in general, e.g. literature
• CPC Class Codes: G10K 2210/511 Narrow band, e.g. implementations for single frequency cancellation
• CPC Class Codes: G10K 2210/512 Wide band, e.g. non-recurring signals
• CPC Class Codes: G10L 21/0208 Noise filtering
• CPC Class Codes: G10L 21/0364 for improving intelligibility
• 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

Abstract

A personal audio device, such as a wireless telephone, includes noise canceling 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 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. The anti-noise signal is adaptively generated to minimize the ambient audio sounds at the error microphone. A processing circuit that performs the adaptive noise canceling (ANC) function also filters one or both of the reference and/or error microphone signals, to bias the adaptation of the adaptive filter in one or more frequency regions to alter a degree of the minimization of the ambient audio sounds at the error microphone.

Claims

1. A personal audio device, comprising:

a personal audio device housing;

a transducer mounted on the housing that reproduces an audio signal including both source audio for playback to a listener and an anti-noise signal to counter the effects of ambient audio sounds in an acoustic output of the transducer;

a reference microphone mounted on the housing that generates a reference microphone signal indicative of the ambient audio sounds;

an error microphone mounted on the housing in proximity to the transducer that generates 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 implements a first adaptive filter having a response that generates the anti-noise signal from the reference microphone signal to reduce the presence of the ambient audio sounds heard by the listener, wherein the processing circuit shapes the response of the first adaptive filter in conformity with the error microphone signal and the reference microphone signal by adapting the response of the first adaptive filter to minimize the ambient audio sounds at the error microphone according to coefficients generated by a coefficient control that receives an error signal derived from the error microphone signal, wherein the error signal is filtered by a filter implemented by the processing circuit to weight one or more particular frequency regions within the response of the first adaptive filter before being provided to the coefficient control, wherein the coefficient control computes the coefficients by correlating the error signal with the reference microphone signal, wherein the filtering of the error signal causes the coefficients to be adjusted to increase or decrease the degree to which the anti-noise signal cancels the ambient audio sounds in the one or more particular frequency regions relative to the degree to which the anti-noise signal cancels the ambient audio sounds in other frequency regions by respectively increasing or decreasing a gain applied to the error signal in the one or more particular frequency regions relative to gain applied to the other frequency regions within the response of the first adaptive filter, wherein the processing circuit further implements a second adaptive filter having a response that generates a shaped source audio signal and a combiner that subtracts the shaped source audio signal from the error microphone signal to generate the error signal, wherein the combiner cancel components of the source audio signal present in the error microphone signal in order to prevent the first adaptive filter from cancelling components of the source audio signal when generating the anti-noise signal, wherein the processing circuit shapes the response of the second adaptive filter in conformity with the source audio signal and the error microphone signal by adapting the response of the second adaptive filter to minimize cancellation of the source audio sounds at the error microphone.

2. The personal audio device of claim 1, wherein a frequency response of the error signal is weighted to compensate for a frequency response of an external acoustic path.

3. The personal audio device of claim 2, wherein a phase response of another signal derived from the reference microphone signal is adjusted to compensate for the weighting of the error signal.

4. The personal audio device of claim 2, wherein the response of the external acoustic channel has one or more multipath nulls, and wherein the error signal is weighted to adjust the shape of the response of the first adaptive filter in the one or more particular frequency regions corresponding to the one or more multipath nulls.

5. The personal audio device of claim 3, wherein an equal weighting is applied to the another signal derived from the reference microphone signal and the error signal.

6. The personal audio device of claim 1, wherein the personal audio device is a wireless telephone further comprising a transceiver for receiving the source audio as a downlink audio signal.

7. 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 to produce a reference microphone signal;

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

adaptively generating an anti-noise signal from a result of the first measuring and the second measuring to minimize the effects of ambient audio sounds at the error microphone by adapting a response of a first 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;

adaptively generating a shaped source audio signal from a result of the second measuring and the source audio signal to minimize cancellation of the source audio sounds at the error microphone by adapting a response of a second adaptive filter that filters the source audio signal to generate the shaped source audio;

subtracting the shaped source audio signal from the error microphone signal to generate an error signal, wherein the subtracting cancels components of the source audio signal present in the error microphone signal from appearing in the error signal, in order to prevent the first adaptive filter from cancelling components of the source audio signal when generating the anti-noise signal;

filtering the error signal to weight one or more particular frequency regions within the response of the first adaptive filter by increasing or decreasing the gain applied to the error signal in one or more particular frequency regions; and

providing a result of the filtering to a coefficient control of the first adaptive filter to shape the amplitude response of the first adaptive filter by correlating the result of the filtering with the reference microphone signal to generate coefficients that control the amplitude response of the first adaptive filter, so that, respective to and in conformity with the increasing or decreasing of the gain applied to the error signal in the one or more particular frequency regions relative to gain applied to other frequency regions within the response of the first adaptive filter, the coefficients are adjusted to increase or decrease the degree to which the anti-noise signal cancels the ambient audio sounds in the one or more particular frequency regions relative to the degree to which the anti-noise signal cancels the ambient audio sounds in the other frequency regions.

8. The method of claim 7, wherein the filtering weights a frequency response of the error signal to compensate for a frequency response of an external acoustic path.

9. The method of claim 8, further comprising adjusting a phase response of another signal derived from the reference microphone signal to compensate for the weighting of the error signal by the filtering.

10. The method of claim 9, wherein the filtering applies an equal weighting to the another signal derived from the reference microphone signal and the error signal.

11. The method of claim 8, wherein the response of the external acoustic channel has one or more multipath nulls, and wherein the filtering weights the error signal to adjust the shape of the response of the first adaptive filter in the one or more particular frequency regions corresponding to the one or more multipath nulls.

12. The method of claim 8, wherein the personal audio device is a wireless telephone, and wherein the method further comprises receiving the source audio as a downlink audio signal.

13. 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 the ambient audio sounds at the transducer; and

a processing circuit that implements a first adaptive filter having a response that generates the anti-noise signal from the reference microphone signal to reduce the presence of the ambient audio sounds heard by the listener, wherein the processing circuit shapes the response of the first adaptive filter in conformity with the error microphone signal and the reference microphone signal by adapting the response of the first adaptive filter to minimize the ambient audio sounds at the error microphone according to coefficients generated by a coefficient control that receives an error signal derived from the error microphone signal, wherein the error signal is filtered by a filter implemented by the processing circuit to weight one or more particular frequency regions within the response of the first adaptive filter before being provided to the coefficient control, wherein the coefficient control computes the coefficients by correlating the error signal with the reference microphone signal, wherein the filtering of the error signal causes the coefficients to be adjusted to increase or decrease the degree to which the anti-noise signal cancels the ambient audio sounds in (the) one or more particular frequency regions relative to the degree to which the anti-noise signal cancels the ambient audio sounds in other frequency regions by respectively increasing or decreasing a gain applied to the error signal in the one or more particular frequency regions relative to gain applied to the other frequency regions within the response of the first adaptive filter, wherein the processing circuit further implements a second adaptive filter having a response that generates a shaped source audio signal and a combiner that subtracts the shaped source audio signal from the error microphone signal to generate the error signal, wherein the combiner cancel components of the source audio signal present in the error microphone signal in order to prevent the first adaptive filter from cancelling components of the source audio signal when generating the anti-noise signal, wherein the processing circuit shapes the response of the second adaptive filter in conformity with the source audio signal and the error microphone signal by adapting the response of the second adaptive filter to minimize cancellation of the source audio sounds at the error microphone.

14. The integrated circuit of claim 13, wherein a frequency response of the error signal is weighted to compensate for a frequency response of an external acoustic path.

15. The integrated circuit of claim 14, wherein a phase response of another signal derived from the reference microphone signal is adjusted to compensate for the weighting of the error signal.

16. The integrated circuit of claim 14, wherein the response of the external acoustic channel has one or more multipath nulls, and wherein the error signal is weighted to adjust the shape of the response of the first adaptive filter in the one or more first particular frequency regions corresponding to the one or more multipath nulls.

17. The integrated circuit of claim 15, wherein an equal weighting is applied to the another signal derived from the reference microphone signal and the error signal.