# US 2019/0379972 A1 · Techniques for howling detection

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- Number: US 2019/0379972 A1
- Document ID: US20190379972A1
- Status: Published application
- Kind: A1
- Application number: 16/004,900
- Filed: 2018-06-11
- Published: 2019-12-12
- Earliest claimed: 2018-06-11
- Assignees: Cirrus Logic International Semiconductor Ltd.
- Applicants: Cirrus Logic International Semiconductor Ltd.
- Inventors: Pablo PESO PARADA; Rahim SAEIDI; John L. MELANSON
- Web page: https://patentgrep.com/patent/US20190379972A1

## CPC

- G10K 11/17819: {between the output signals and the reference signals, e.g. to prevent howling}
- H04R 3/02: for preventing acoustic reaction {, i.e. acoustic oscillatory feedback (specially adapted for hearing aids H04R25/453)}
- G10K 11/17835: {using detection of abnormal input signals}
- G10K 11/17881: {the reference signal being an acoustic signal, e.g. recorded with a microphone}
- H04M 1/20: Arrangements for preventing acoustic feed-back (H04M1/62 takes precedence)
- G10K 2210/108: Communication systems, e.g. where useful sound is kept and noise is cancelled
- G10K 2210/3056: Variable gain
- G10K 2210/503: Diagnostics; Stability; Alarms; Failsafe
- H04R 2460/01: Hearing devices using active noise cancellation
- H04R 2499/11: Transducers incorporated or for use in hand-held devices, e.g. mobile phones, PDA's, camera's
- 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
- 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)
- H04M: TELEPHONIC COMMUNICATION (circuits for controlling other apparatus via a telephone cable and not involving telephone switching apparatus G08)

## Abstract

The application describes techniques for howling detection. A processing module for a noise control circuit is described. The processing module comprises a howling detector configured to receive an input signal and to determine a log-linearity metric based on the input signal. Gain adjustment of the noise control unit following the detection of howling is also described, wherein the amount of gain adjustment may be based on an estimation of the maximum stable gain of the noise control unit.

## Claims

### Claim 1

A processing module for a noise control circuit, the processing module comprising:
a howling detector configured to receive an input signal and to determine a linearity metric based on the input signal, the linearity metric comprising a measure of the linearity of a logarithmic representation of the energy of the input signal; and
a gain adjuster configured to adjust the gain of a noise control unit.

### Claim 2 (depends on 1)

The processing module as claimed in claim 1, wherein the linearity metric is derived by computing a difference between the logarithm of the energy of the signal and a trend line, the trend line being is a straight line representation of the logarithm of the energy of the signal.

### Claim 3 (depends on 2)

The processing module as claimed in claim 2, wherein coefficients of the trend line are derived by a fitting a line to the logarithmic representation of the energy of the input signal.

### Claim 4 (depends on 3)

The processing module as claimed in claim 3, wherein fitting a line to the logarithmic representation of the energy of the input signal comprises performing a least squares computation which minimises a difference between the trend line and the logarithmic representation of the energy of the input signal.

### Claim 5 (depends on 2)

The processing module as claimed in claim 2, wherein the linearity metric is determined according to a goodness of fit measure of the computed trend line to the logarithm of the energy of the input signal over P samples.

### Claim 6 (depends on 5)

The processing module as claimed in claim 5, wherein the goodness of fit measure r(n) is be represented by:
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where y(n) is the log energy of the input signal, {circumflex over (β)}0(n) is the bias of the trend line and {circumflex over (β)}1(n) is the slope of the trend line.

### Claim 7 (depends on 1)

The processing module as claimed in claim 1, wherein the howling detection unit is further configured to issue a command to the gain adjuster in order to reduce the gain if the linearity metric exceeds a predetermined threshold.

### Claim 8 (depends on 7)

The processing module as claimed in claim 7, wherein the gain adjuster is configured to adjust the gain by a fixed amount.

### Claim 9 (depends on 1)

The processing module as claimed in claim 1, wherein the howling detection unit is further configured to estimate a maximum stable gain of the noise control unit.

### Claim 10 (depends on 2)

The processing module as claimed in claim 2, wherein the howling detection unit is further configured to estimate a maximum stable gain of the noise control unit, and wherein the maximum stable gain is proportional to the slope of the trend line.

### Claim 11 (depends on 1)

The processing module as claimed in claim 1, wherein the howling detection unit is configured to determine, based on the determined linearity metric, if howling is likely or imminent.

### Claim 12 (depends on 1)

An audio processing system comprising the processing module as claimed in claim 1 and further comprising a noise control unit for generating a noise control signal based on a reference input signal which represents a sound detected by a reference microphone.

### Claim 13 (depends on 12)

The audio processing system as claimed in claim 12, wherein the processing module is connected to a speaker and wherein the speaker generates an anti-noise signal based on the noise control signal in order to cancel or at least reduce the noise detected by a reference microphone.

### Claim 14 (depends on 13)

The audio processing system as claimed in claim 13, wherein the howling detector is provided in parallel with the noise control unit.

### Claim 15 (depends on 1)

A audio processing module as claimed in claim 1, further comprising a filter configured to filter out one or more frequencies or frequency bands of the input signal.

### Claim 16 (depends on 1)

A audio processing module as claimed in claim 1, further comprising a filterbank configured to split the input signal into a plurality of frequency bands, wherein the howling detector is operable to determine a linearity metric for each frequency band.

### Claim 17

A processing circuit for a noise control module comprising:
a gain adjustment mechanism configured to adjust the gain of a noise control circuit if a plot of the energy of an input signal in the log domain becomes linear or tends towards linearity.

### Claim 18 (depends on 17)

The processing circuit as claimed in claim 17, wherein the gain of the noise control circuit is adjusted by an amount that related to a difference between a measure of the linearity of the plot of the energy of the input signal in the log domain and a target linearity metric.

### Claim 19 (depends on 1)

The processing module as claimed in claim 1, in the form of a monolithic integrated circuit.

### Claim 20 (depends on 1)

A device comprising a processing module according to claim 1, wherein the device comprises a mobile telephone, headphone, acoustic noise cancelling headphones, a smart watch, an audio player, a video player, a mobile computing platform, a games device, a remote controller device, a toy, a machine, or a home automation controller, a domestic appliance or other portable device.

### Claim at position 21

21-22. (canceled)