Adaptive noise canceling architecture for a personal audio device

Patent metadata

Field	Value
Publication number	US-9318094-B2
Application number	US-201213413920-A
Country	US
Kind code	B2
Filing date	Mar 7, 2012
Priority date	Jun 3, 2011
Publication date	Apr 19, 2016
Grant date	Apr 19, 2016

Abstract

A personal audio device, such as a wireless telephone, includes an adaptive noise canceling (ANC) circuit that adaptively generates an anti-noise signal from a reference microphone signal that measures the ambient audio and an error microphone signal that measures the output of an output transducer plus any ambient audio at that location and injects the anti-noise signal at the transducer output to cause cancellation of ambient audio sounds. A processing circuit uses the reference and error microphone to generate the anti-noise signal, which can be generated by an adaptive filter operating at a multiple of the ANC coefficient update rate. Downlink audio can be combined with the high data rate anti-noise signal by interpolation. High-pass filters in the control paths reduce DC offset in the ANC circuits, and ANC coefficient adaptation can be halted when downlink audio is not detected.

First claim

What is 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 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 processing circuit that implements an 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 implements a coefficient control block that shapes the response of the adaptive filter in conformity with the error microphone signal and the reference microphone signal by adapting the response of the adaptive filter to minimize the ambient audio sounds at the error microphone, wherein a first sample rate of the adaptive filter is substantially higher than a second sample rate at which the coefficient control block operates, wherein the source audio has a sample rate equal to or less than the second sample rate;
an interpolator included in the processing circuit that converts the source audio to the first sample rate; and
a combiner included in the processing circuit that combines the anti-noise signal and an output of the interpolator to generate the audio signal at the first sample rate.

2. The personal audio device of claim 1 , wherein the processing circuit implements a secondary path adaptive filter having a secondary path response that shapes the source audio and another 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, wherein the secondary path adaptive filter is also operated at the first sample rate, and wherein updates of coefficients of the secondary path adaptive filter are performed at a rate equal to or lower than the second sample rate.

3. 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 a result of the second measuring for countering the effects of the ambient audio sounds at an acoustic output of the transducer by adapting a response of an 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, wherein the anti-noise signal is generated at a first sample rate that is substantially higher than a second sample rate of a coefficient control of the adaptive filter, wherein the source audio has a sample rate equal to or less than the second sample rate;
converting the source audio to the first sample rate by interpolation; and
combining the anti-noise signal and a result of the converting to generate the audio signal at the first sample rate.

4. The method of claim 3 , further comprising:
shaping a copy of the source audio with a secondary path response with a secondary path adaptive filter operating at the first sample rate;
removing the result of the shaping the copy of the source audio from the error microphone signal to produce an error signal indicative of the combined anti-noise and ambient audio sounds; and
updating coefficients of the secondary path adaptive filter at a rate equal to or lower than the second sample rate.

5. 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 acoustic output of the transducer and the ambient audio sounds at the transducer;
a processing circuit that implements an 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 implements a coefficient control block that shapes the response of the adaptive filter in conformity with the error microphone signal and the reference microphone signal by adapting the response of the adaptive filter to minimize the ambient audio sounds at the error microphone, wherein a first sample rate of the adaptive filter is substantially higher than a second sample rate at which the coefficient control block operates, wherein the source audio has a sample rate equal to or less than the second sample rate;
an interpolator included in the processing circuit that converts the source audio to the first sample rate; and
a combiner included in the processing circuit that combines the anti-noise signal and an output of the interpolator to generate the audio signal at the first sample rate.

6. The integrated circuit of claim 5 , wherein the processing circuit implements a secondary path adaptive filter having a secondary path response that shapes the source audio and another 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, wherein the secondary path adaptive filter is also operated at the first sample rate, and wherein updates of coefficients of the secondary path adaptive filter are performed at a rate equal to or lower than the second sample rate.

7. A personal audio device, comprising:
a personal audio device housing;
an audio source having an output providing source audio for playback to a listener;
a transducer mounted on the housing for reproducing an audio signal;
a combiner for combining the source audio and an anti-noise signal for countering the effects of ambient audio sounds in an acoustic output of the transducer, to generate the audio signal;
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 implements an 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 implements a coefficient control block that shapes the response of the adaptive filter by adjusting coefficients that determine the response of the adaptive filter in conformity with the error microphone signal and the reference microphone signal to minimize the ambient audio sounds at the error microphone, wherein the processing circuit detects whether or not the source audio is present at the output of the audio source, and in response to dete

Assignees

• Hendrix Jon D
• Kamath Gautham Devendra
• Kwatra Nitin
• Abdollahzadeh Milani Ali
• Alderson Jeffrey
• Cirrus Logic Inc

Inventors

• Hendrix Jon D
• Kamath Gautham Devendra
• Kwatra Nitin
• Abdollahzadeh Milani Ali
• Alderson Jeffrey

Classifications

• H04R1/1083

  Reduction of ambient noise (active noise reduction per se G10K11/175; protective devices for the ear, e.g. providing acoustic protection A61F11/06) · CPC title

• G10K2210/3026

  Feedback · CPC title

• G10K2210/3055

  Transfer function of the acoustic system · CPC title

• H04R3/005

  for combining the signals of two or more microphones (specially adapted for hearing aids H04R25/407) · CPC title

• G10K2210/3051

  Sampling, e.g. variable rate, synchronous, decimated or interpolated · CPC title