# US 11,445,306 B2 · Method and apparatus for robust acoustic feedback cancellation

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- Number: US 11,445,306 B2
- Document ID: US11445306B2
- Status: Granted
- Kind: B2
- Application number: 15/687,025
- Filed: 2017-08-25
- Published: 2018-03-01
- Granted: 2022-09-13
- Earliest claimed: 2016-08-26
- Assignees: Starkey Laboratories, Inc.
- Applicants: Starkey Laboratories, Inc.
- Inventors: Carlos Renato Calcada Nakagawa; Karim Helwani; Ivo Merks
- Web page: https://patentgrep.com/patent/US11445306B2

## CPC

- H04R 25/453: {electronically}
- G10K 11/178: by electro-acoustically regenerating the original acoustic waves in anti-phase
- G10K 11/17854: {the filter being an adaptive filter}
- H04R 3/02: for preventing acoustic reaction {, i.e. acoustic oscillatory feedback (specially adapted for hearing aids H04R25/453)}
- H04R 25/43: {Electronic input selection or mixing based on input signal analysis, e.g. mixing or selection between microphone and telecoil or between microphones with different directivity characteristics (H04R25/407 takes precedence)}
- H04R 25/505: {using digital signal processing}
- G10K 2210/108: Communication systems, e.g. where useful sound is kept and noise is cancelled
- H04R: LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; ELECTRIC HEARING AIDS; PUBLIC ADDRESS SYSTEMS (producing sounds with frequency not determined by supply frequency G10K)
- 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

The present subject matter can improve robustness of performance of acoustic feedback cancellation in the presence of strong acoustic disturbances. In various embodiments, an optimization criterion determined to enhance robustness of an adaptive feedback canceller in an audio device against disturbances in an incoming audio signal can be applied such that the adaptive feedback canceller remains in a converged state in response to presence of the disturbances.

## Claims

### Claim 1

A method for adaptive acoustic feedback cancellation in an audio device, comprising:
applying an optimization criterion determined to enhance robustness of an adaptive feedback canceller of the audio device by keeping disturbances in an incoming audio signal of the audio device from resulting in divergence of the adaptive feedback canceller, the adaptive feedback canceller configured to produce an estimate of a feedback signal, the disturbances including onsets of the incoming audio signal of the audio device, the application of the optimization criterion maintaining the adaptive feedback canceller in a converged state in presence of the disturbances, including detecting the onsets of the incoming audio signal using a threshold and adjusting the adaptive feedback canceller using an error signal resulting from subtracting the estimate of the feedback signal from the incoming audio signal in response to each detection of the onsets of the incoming audio signal,
wherein adjusting the adaptive feedback canceller using the error signal includes constraining the error signal and updating the adaptive feedback canceller using the constrained error signal.

### Claim 2 (depends on 1)

The method of claim 1, further comprising receiving the incoming audio signal from a microphone.

### Claim 3 (depends on 2)

The method of claim 2, wherein applying the optimization criterion comprises minimizing a non-quadratic cost function.

### Claim 4 (depends on 3)

The method of claim 3, further comprising applying a prediction error method to whiten the error signal prior to constraining the error signal.

### Claim 5 (depends on 4)

The method of claim 4, wherein constraining the error signal comprises limiting and scaling the error signal.

### Claim 6 (depends on 4)

The method of claim 4, wherein the non-quadratic cost function is:
J
=
E
⁢
{
ϱ
⁡
(

e
f
⁡
(
n
)

s
)
}
,
where E{·} is the energy, Ω (·) is a symmetric function with a monotonically non-decreasing derivative, s is a scale factor, and ef(n) is the pre-whitened error signal.

### Claim 7 (depends on 1)

The method of claim 1, further comprising halting an adaptation process of the adaptive feedback canceller in response to each detection of the onsets of the incoming audio signal.

### Claim 8

A method for operating a processor of an audio device for adaptive acoustic feedback cancellation, comprising:
operating an adaptive feedback canceller of the processor in a converged state, including producing an estimate of a feedback signal;
producing an error signal by subtracting h estimate of the feedback signal ro an incoming audio signal;
detecting onsets of the incoming audio signal received by the audio device using a threshold; and
adjusting the adaptive feedback canceller using the error signal to maintain the adaptive feedback canceller in the converged state in response to a detection of each of the onsets of the incoming audio signal by keeping the detected onset of the incoming audio signal from resulting in divergence of the adaptive feedback canceller,
wherein adjusting the adaptive feedback canceller using the error signal includes constraining the error signal and updating the adaptive feedback canceller using the constrained error signal.

### Claim 9 (depends on 8)

The method of claim 8, wherein adjusting the adaptive feedback canceller comprises halting an adaptation process of the adaptive feedback canceller for a period following the detection of each of the onsets of the incoming audio signal.

### Claim 10 (depends on 9)

The method of claim 9, wherein operating the adaptive feedback canceller comprises operating an adaptive filter, and adjusting the adaptive feedback canceller comprises adjusting the adaptive filter for robustness against each of the onsets of the incoming audio signal.

### Claim 11 (depends on 10)

The method of claim 10, further comprising applying a prediction error method to whiten the error signal prior to constraining the error signal.

### Claim 12 (depends on 11)

The method of claim 11, wherein constraining the error signal comprises limiting and scaling the error signal.

### Claim 13 (depends on 8)

The method of claim 8, further comprising:
receiving the incoming audio signal using a microphone of the audio device;
producing an output signal by processing the incoming audio signal using the processor; and
produce an output sound using a loudspeaker of the audio device using the output signal.

### Claim 14

An audio device, comprising:
a microphone configured to receive an input sound and to produce a microphone signal representative of the received sound;
an audio processing circuit configured to process the microphone sound to produce a loudspeaker signal, the audio processing circuit including an adaptive feedback canceller configured to cancel acoustic feedback in the microphone signal and configured to produce a feedback estimate being an estimate of the acoustic feedback in the microphone signal, to constrain an error signal being a difference between the microphone signal and the feedback estimate, and to be updated using the constrained error signal by applying an optimization criterion determined to enhance robustness by keeping disturbances in the microphone signal from resulting in divergence of the adaptive feedback canceller, the disturbances including onsets of the microphone signal, such that the adaptive feedback canceller remains convergent in the presence of the disturbances, the audio processing circuit configured to detect the onsets of the microphone signal using a threshold and to adjust the adaptive feedback canceller in response to each detection of the onsets of the microphone signal; and
a loudspeaker configured to produce an output sound using the loudspeaker signal.

### Claim 15 (depends on 14)

The audio device of claim 14, wherein the audio device comprises a hearing device.

### Claim 16 (depends on 15)

The audio device of claim 15, wherein the hearing device comprises a hearing aid configured to compensate for hearing impairment.

### Claim 17 (depends on 14)

The audio device of claim 14, wherein the audio processing circuit comprises an adaptive filter including:
filter circuitry configured to produce the feedback estimate;
gradient estimator circuitry configured to constrain the error signal and to produce a gradient estimate using the constrained error signal; and
update filter circuitry configured to update coefficients of filter circuitry using the produced gradient estimate.

### Claim 18 (depends on 17)

The audio device of claim 17, wherein the gradient estimator circuitry comprises:
limiter circuitry configured to limit the error signal;
scale factor circuitry configured to apply a scale factor to the error signal; and
sign circuitry configured to determine a sign of the error signal.

### Claim 19 (depends on 18)

The audio device of claim 18, wherein the audio processing circuit is configured to apply a prediction error method to whiten the error signal, and the gradient estimator circuitry is configured to receive and constrain the whitened error signal.

### Claim 20 (depends on 14)

The audio device of claim 14, wherein the audio processing circuit is configured to halt an adaptation process of the adaptive feedback canceller in response to each detection of the onsets of the microphone signal.