# US 2017/0256248 A1 · Systems and methods for controlling adaptive noise control gain

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- Number: US 2017/0256248 A1
- Document ID: US20170256248A1
- Status: Published application
- Kind: A1
- Application number: 15/058,866
- Filed: 2016-03-02
- Published: 2017-09-07
- Earliest claimed: 2016-03-02
- Assignees: Cirrus Logic International Semiconductor Ltd.
- Applicants: Cirrus Logic International Semiconductor Ltd.
- Inventors: Jeffrey D. Alderson; Jon D. Hendrix; Sang-Ik Terry Cho; Chin Huang Yong; John L. Melanson
- Web page: https://patentgrep.com/patent/US20170256248A1

## CPC

- G10K 11/17854: {the filter being an adaptive filter}
- G10K 11/17813: {characterised by the analysis of the acoustic paths, e.g. estimating, calibrating or testing of transfer functions or cross-terms}
- G10K 11/17815: {between the reference signals and the error signals, i.e. primary path}
- G10K 11/17881: {the reference signal being an acoustic signal, e.g. recorded with a microphone}
- G10K 11/17885: {additionally using a desired external signal, e.g. pass-through audio such as music or speech}
- G10K 2210/108: Communication systems, e.g. where useful sound is kept and noise is cancelled
- G10K 2210/1081: Earphones, e.g. for telephones, ear protectors or headsets
- G10K 2210/3014: Adaptive noise equalizers [ANE], i.e. where part of the unwanted sound is retained
- G10K 2210/3016: Control strategies, e.g. energy minimization or intensity measurements
- G10K 2210/3028: Filtering, e.g. Kalman filters or special analogue or digital filters
- G10K 2210/3056: Variable gain
- G10K: SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR

## Abstract

A method may include adaptively generating an anti-noise signal for countering the effects of ambient audio sounds at an acoustic output of the transducer by adapting a response of an adaptive filter that filters a reference microphone signal in conformity with an error microphone signal and the reference microphone signal to minimize the ambient audio sounds in the error microphone, generating a scaled anti-noise signal by applying a scaling factor to the anti-noise signal, further adjusting the response of the adaptive filter independent of a source audio signal by altering an input to the coefficient control block of the adaptive filter to compensate for the scaling factor, and combining the scaled anti-noise signal with the source audio signal to generate an audio signal provided to the transducer.

## Claims

### Claim 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 a scaled anti-noise signal for countering the 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 comprising:
an adaptive filter having a response that generates an unscaled anti-noise signal from the reference microphone signal to reduce the presence of the ambient audio sounds heard by the listener;
a scaling portion that generates the scaled anti-noise signal by applying a scaling factor to the anti-noise signal;
a coefficient control block that shapes the response of the adaptive filter in conformity with the reference microphone signal and the error microphone signal by adapting the response of the adaptive filter to minimize the ambient audio sounds at the error microphone signal; and
a biasing portion configured to further adjust the response of the adaptive filter independent of the source audio signal by altering an input to the coefficient control block of the adaptive filter to compensate for the scaling factor.

### Claim 2 (depends on 1)

The integrated circuit of claim 1, wherein:
the processing circuit further comprises a secondary path estimate filter configured to model an electro-acoustic path of the source audio signal;
the biasing portion generates an unscaled filtered anti-noise signal by applying a second scaling factor to the response of the secondary path estimate filter to the scaled anti-noise signal; and
the coefficient control block shapes the response of the adaptive filter in conformity with the reference microphone signal and a modified playback corrected error signal by adapting the response of the adaptive filter to minimize the ambient audio sounds in the error microphone signal, wherein the playback corrected error is based on a difference between the error microphone signal and the source audio signal and the modified playback corrected error signal is based on a difference between the playback corrected error signal and the unscaled filtered anti-noise signal.

### Claim 3 (depends on 2)

The integrated circuit of claim 2, wherein the second scaling factor defines a gain, wherein the gain is the ratio of a filtered anti-noise signal generated by the secondary path estimate filter to the unscaled filtered anti-noise generated by the second scaling portion.

### Claim 4 (depends on 2)

The integrated circuit of claim 2, wherein the second scaling factor is a function of the scaling factor.

### Claim 5 (depends on 4)

The integrated circuit of claim 4, wherein the second scaling factor is approximately equal to one minus the inverse of the scaling factor.

### Claim 6 (depends on 1)

The integrated circuit of claim 1, wherein the biasing portion generates an injected noise that is combined with an input to the coefficient control block so that the response of the adaptive filter is biased by the coefficient control block adapting to attenuate the injected noise.

### Claim 7 (depends on 6)

The integrated circuit of claim 6, wherein the biasing portion further comprises a copy of the adaptive filter to receive the injected noise and the output of the copy of the adaptive filter is removed from the error microphone signal.

### Claim 8 (depends on 6)

The integrated circuit of claim 6, wherein the processing circuit further comprises a secondary path adaptive filter having a secondary path response that shapes the source audio signal and a combiner that removes the shaped source audio signal from the error microphone signal to provide a playback corrected error signal indicative of the generated anti-noise delivered to the listener and the ambient audio sounds, and wherein the processing circuit shapes the response of the adaptive filter in conformity with the playback corrected error signal and the reference microphone signal.

### Claim 9 (depends on 6)

The integrated circuit of claim 6, wherein the biasing portion applies a second scaling factor to the injected noise to control the injected noise.

### Claim 10 (depends on 9)

The integrated circuit of claim 9, wherein the second scaling factor is a function of the scaling factor.

### Claim 11 (depends on 10)

The integrated circuit of claim 10, wherein the second scaling factor is approximately inversely proportional to the scaling factor.

### Claim 12 (depends on 1)

The integrated circuit of claim 1, wherein the scaling factor has a value between 0 and 1.

### Claim 13 (depends on 1)

The integrated circuit of claim 1, wherein the scaling factor defines a gain, wherein the gain is the ratio of the anti-noise signal generated by the adaptive filter to the scaled anti-noise generated by the scaling portion.

### Claim 14 (depends on 1)

The integrated circuit of claim 1, wherein the scaling factor is tunable in response to an ambient audio event.

### Claim 15 (depends on 1)

The integrated circuit of claim 1, wherein the scaling factor is controllable by a user of the personal audio device.

### Claim 16 (depends on 15)

The integrated circuit of claim 15, wherein the scaling factor is controllable in response to user interaction with a user interface of the personal audio device.

### Claim 17 (depends on 15)

The integrated circuit of claim 15, wherein the scaling factor is controllable in response to a voice command uttered by a user of the personal audio device.

### Claim 18

A method comprising:
receiving a reference microphone signal indicative of ambient audio sounds;
receiving an error microphone signal indicative of an output of a transducer and the ambient audio sounds at the transducer;
generating a source audio signal for playback to a listener;
adaptively generating an anti-noise signal for countering the effects of ambient audio sounds at an acoustic output of the transducer by adapting a response of an adaptive filter that filters the reference microphone signal in conformity with the error microphone signal and the reference microphone signal to minimize the ambient audio sounds in the error microphone;
generating a scaled anti-noise signal by applying a scaling factor to the anti-noise signal;
further adjusting the response of the adaptive filter independent of the source audio signal by altering an input to a coefficient control block of the adaptive filter to compensate for the scaling factor; and
combining the scaled anti-noise signal with the source audio signal to generate an audio signal provided to the transducer.

### Claim 19 (depends on 18)

The method of claim 18, further comprising:
generating an unscaled filtered anti-noise signal by applying a second scaling factor to a response of a secondary path estimate filter to the scaled anti-noise signal, wherein the secondary path estimate filter configured models an electro-acoustic path of the source audio signal; and
shaping the response of the adaptive filter in conformity with the reference microphone signal and a modified playback corrected error signal by adapting the response of the adaptive filter to minimize the ambient audio sounds in the error microphone signal, wherein the playback corrected error is based on a difference between the error microphone signal and the source audio signal and the modified playback corrected error signal is based on a difference between the playback corrected error signal and an unscaled filtered anti-noise signal.

### Claim 20 (depends on 19)

The method of claim 19, wherein the second scaling factor defines a gain, wherein the gain is the ratio of a filtered anti-noise signal generated by the secondary path estimate filter to the unscaled filtered anti-noise generated by the second scaling portion.

### Claim 21 (depends on 19)

The method of claim 19, wherein the second scaling factor is a function of the scaling factor.

### Claim 22 (depends on 21)

The method of claim 21, wherein the second scaling factor is approximately equal to one minus the inverse of the scaling factor.

### Claim 23 (depends on 18)

The method of claim 18, further comprising generating an injected noise that is combined with an input to the coefficient control block so that the response of the adaptive filter is biased by the coefficient control block adapting to attenuate the injected noise.

### Claim 24 (depends on 23)

The method of claim 23, further comprising:
receiving the injected noise by a copy of the adaptive filter; and
removing an output of the copy of the adaptive filter from the error microphone signal.

### Claim 25 (depends on 23)

The method of claim 23, further comprising:
shaping the source audio signal with a secondary path adaptive filter having a secondary path response;
removing the shaped source audio signal from the error microphone signal to provide a playback corrected error signal indicative of the generated anti-noise delivered to the listener and the ambient audio sounds; and
shaping the response of the adaptive filter in conformity with the playback corrected error signal and the reference microphone signal.

### Claim 26 (depends on 23)

The method of claim 23, further comprising applying a second scaling factor to the injected noise to control the injected noise.

### Claim 27 (depends on 26)

The method of claim 26, wherein the second scaling factor is a function of the scaling factor.

### Claim 28 (depends on 27)

The method of claim 27, wherein the second scaling factor is approximately inversely proportional to the scaling factor.

### Claim 29 (depends on 18)

The method of claim 18, wherein the scaling factor has a value between 0 and 1.

### Claim 30 (depends on 18)

The method of claim 18, wherein the scaling factor defines a gain, wherein the gain is the ratio of the anti-noise signal generated by the adaptive filter to the scaled anti-noise generated by the scaling portion.

### Claim 31 (depends on 18)

The method of claim 18, wherein the scaling factor is tunable in response to an ambient audio event.

### Claim 32 (depends on 18)

The method of claim 18, wherein the scaling factor is controllable by a user of a personal audio device comprising or communicatively coupled to the transducer.

### Claim 33 (depends on 32)

The method of claim 32, wherein the scaling factor is controllable in response to user interaction with a user interface of the personal audio device.

### Claim 34 (depends on 32)

The method of claim 32, wherein the scaling factor is controllable in response to a voice command uttered by a user of the personal audio device.