Robust adaptive noise canceling (ANC) in a personal audio device

Patent metadata

Field	Value
Publication number	US-9502020-B1
Application number	US-201414210589-A
Country	US
Kind code	B1
Filing date	Mar 14, 2014
Priority date	Mar 15, 2013
Publication date	Nov 22, 2016
Grant date	Nov 22, 2016

Abstract

An adaptive noise canceling (ANC) circuit adaptively generates an anti-noise signal that is injected into the speaker or other transducer output to cause cancellation of ambient audio sounds. At least one microphone provides an error signal indicative of the noise cancellation at the transducer, and the adaptive filter is adapted to minimize the error signal. In order to prevent improper adaptation or instabilities in one or both of the adaptive filters, spikes are detected in the error signal by comparing the error signal or its rate of change to a threshold. Therefore, if the magnitude of the coefficient error is greater than a threshold value for an update, the update is skipped. Alternatively the step size of the updates may be reduced. Similar criteria can be applied to a filter modeling the secondary path, based on detection applied to both the source audio and the error signal.

First claim

The invention claimed is:

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 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; and
a processing circuit that adaptively generates the anti-noise signal from the reference microphone signal by adapting a first adaptive filter 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 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 adapts first coefficients of the first adaptive filter according to the reference microphone signal and the error signal and adapts second coefficients of the secondary path adaptive filter according to the error signal, and wherein if a magnitude of a value derived from the error microphone signal has a rate of change that exceeds a threshold value indicating a spike in the ambient audio sounds, the processing circuit alters adaptation of the first adaptive filter to reduce disruption in values of the coefficients caused by the spike in the ambient audio sounds.

2. The personal audio device of claim 1 , wherein the processing circuit determines an average level of the ambient audio sounds from an average of the value derived from the error microphone signal, and determines the rate of change of the magnitude of the value derived from the error microphone signal from a difference between the average level of the value derived from the error microphone signal and an instantaneous value of the magnitude of the value derived from the error microphone signal.

3. The personal audio device of claim 1 , wherein the processing circuit determines an average level of the ambient audio sounds from an average of a value derived from the reference microphone signal, and determines the rate of change of the magnitude of the value derived from the error microphone signal from a difference between the average level of the value derived from the reference microphone signal and an instantaneous value of the magnitude of the value derived from the error microphone signal.

4. The personal audio device of claim 3 , wherein the processing circuit further implements a controllable filter controlled by a coefficient control of the secondary path adaptive filter that filters the reference microphone signal to apply a copy of the secondary path response to the reference microphone signal, wherein the processing circuit determines the average level of the ambient audio sounds from an average value of the output of the controllable filter.

5. The personal audio device of claim 1 , wherein the processing circuit compares the magnitude of the value derived from the error microphone signal to the threshold value at each sample of the error microphone signal, wherein the processing circuit skips updates due to samples for which the magnitude of the value of derived from the error microphone signal exceeds the threshold value.

6. The personal audio device of claim 1 , wherein the processing circuit alters adaptation of the first adaptive filter by freezing adaptation of the first coefficients of the first adaptive filter.

7. The personal audio device of claim 1 , wherein the processing circuit alters adaptation of the first adaptive filter by reducing a step size of the first adaptive filter until the spike is absent from the value derived from the error microphone signal.

8. The personal audio device of claim 1 , wherein the processing circuit implements a counter that sustains the altering of the adaptation of the first adaptive filter after the rate of change of the value derived from the error microphone signal is less than the threshold value for a number of samples equal to or greater than a filter length of the first adaptive filter.

9. The personal audio device of claim 1 , wherein the processing circuit further alters adaptation of the secondary path adaptive filter in response to the magnitude of the value derived from the error microphone signal having a rate of change that exceeds the threshold value indicating the spike in the ambient audio sounds.

10. The personal audio device of claim 1 , wherein the processing circuit further determines if the source audio signal has a rate of change that exceeds a second threshold value indicating a spike in the source audio, the processing circuit alters adaptation of the secondary path adaptive filter to reduce disruption in values of the second coefficients that control adaptation of the secondary path adaptive filter caused by the spike in the source audio.

11. The personal audio device of claim 10 , wherein the processing circuit determines an average level of the source audio, and determines the rate of change of the source audio from a difference between the average level of the source audio and an instantaneous value of the magnitude of the value derived from the error microphone signal.

12. A method of countering effects of ambient audio sounds by a personal audio device, the method comprising:
adaptively generating an anti-noise signal from a reference microphone signal by adapting a first adaptive filter to reduce the presence of the ambient audio sounds heard by the listener in conformity with an error microphone signal and the reference microphone signal;
combining the anti-noise signal with source audio;
providing a result of the combining to a transducer;
generating the reference microphone signal indicative of the ambient audio sounds with a reference microphone;
generating the error microphone signal indicative of audio reproduced by the transducer the transducer and the ambient audio sounds with an error microphone;
filtering the source audio with a secondary path adaptive filter having a secondary path response to produce filtered source audio;
removing the filtered source audio from the error microphone signal to generate an error signal;
adapting first coefficients of the first adaptive filter according to the reference microphone signal and the error signal;
adapting second coefficients of the secondary path adaptive filter according to the error signal;
detecting a spike in the ambient audio sounds by determining whether the magnitude of a value derived from the error microphone signal has a rate of change that exceeds a threshold value; and
responsive to the detecting having detected a spike, altering the adapting of the first coefficients and the second coefficients to reduce disruption in values of the coefficients caused by the spike.

13. The method of claim 12 , further comprising:
determining an average level of the ambient audio sounds from an average of the value derived from the error microphone signal; and
determining the rate of change of the magnitude of the value derived from the error microphone signal from a difference between the average level of the value derived from the error microphone signal and an instantaneous value of the magnitude of the value derived from the e

Assignees

• Cirrus Logic Inc

Inventors

• Abdollahzadeh Milani Ali
• Alderson Jeffrey
• Kamath Gautham Devendra
• Lu Yang

Classifications

• G10K11/16 Primary

  Methods or devices for protecting against, or for damping, noise or other acoustic waves in general (G10K11/36 takes precedence) · CPC title

• G10K11/17881

  the reference signal being an acoustic signal, e.g. recorded with a microphone · CPC title

• G10K2210/3045

  Multiple acoustic inputs, single acoustic output · CPC title

• G10K11/17885

  additionally using a desired external signal, e.g. pass-through audio such as music or speech · CPC title

• G10K11/17854

  the filter being an adaptive filter · CPC title