# US 10,482,895 B2 · Acoustic echo cancellation (AEC) rate adaptation

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- Number: US 10,482,895 B2
- Document ID: US10482895B2
- Status: Granted
- Kind: B2
- Application number: 15/693,726
- Filed: 2017-09-01
- Published: 2019-03-07
- Granted: 2019-11-19
- Earliest claimed: 2017-09-01
- Assignees: Cirrus Logic, Inc.
- Applicants: Cirrus Logic International Semiconductor Ltd.
- Inventors: Khosrow Lashkari; Justin Allen
- Web page: https://patentgrep.com/patent/US10482895B2

## CPC

- G10L 21/0232: Processing in the frequency domain
- G10L 21/0208: Noise filtering
- G10L 25/21: the extracted parameters being power information
- H04B 3/23: using a replica of transmitted signal in the time domain, e.g. echo cancellers
- H04M 9/082: {using echo cancellers (echo cancellers per se H04B3/23)}
- H04R 3/02: for preventing acoustic reaction {, i.e. acoustic oscillatory feedback (specially adapted for hearing aids H04R25/453)}
- H04R 3/04: for correcting frequency response
- G10L 25/51: for comparison or discrimination
- G10L 2021/02082: {the noise being echo, reverberation of the speech}
- G10L 2021/02163: {Only one microphone}
- H04R 2499/11: Transducers incorporated or for use in hand-held devices, e.g. mobile phones, PDA's, camera's
- G10L: SPEECH ANALYSIS TECHNIQUES OR SPEECH SYNTHESIS; SPEECH RECOGNITION; SPEECH OR VOICE PROCESSING TECHNIQUES; SPEECH OR AUDIO CODING OR DECODING
- H04B: TRANSMISSION
- H04M: TELEPHONIC COMMUNICATION (circuits for controlling other apparatus via a telephone cable and not involving telephone switching apparatus G08)
- 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)

## Abstract

Step size can be used to slow or freeze the adaptive filter to improve AEC system performance, such as during double talk events. An AEC control system may be used to adjust the step size based on an echo-to-disturbance energy ratio (EDER). The algorithm adjusts the step size to lower the adaptation rate when the EDER is small (or the combination of the near signal and noise is large compared to the echo) and raise the adaptation rate when the EDER is large (echo is large compared to a combination of near signal and noise).

## Claims

### Claim 1

A method for echo cancellation in an audio system having a transducer and a microphone, comprising:
generating an echo-cancelled output signal from a microphone input signal and a transducer output signal, wherein the echo-cancelled output signal is generated using an adaptive filter;
determining an echo-to-disturbance energy ratio by comparing an energy of the microphone input signal and an energy of the echo-cancelled output signal; and
adjusting a step size of the adaptive filter used to converge on the echo-cancelled output signal based, at least in part, on the echo-to-disturbance energy ratio, wherein the step size is an echo-signal-to-noise-ratio (ESNR)-based variable step size (EVSS) μESNR computed according to:
μ
EVSS
=
μ
⁡
(
P
in
-
P
out
)
P
in
+
(
R
-
1
)
⁢
P
out
.

### Claim 2 (depends on 1)

The method of claim 1, further comprising:
detecting convergence of the adaptive filter; and
performing the step of adjusting the step size based on a convergence state of the adaptive filter.

### Claim 3 (depends on 2)

The method of claim 2, wherein the step of detecting convergence of the adaptive filter comprises comparing a ratio of outputs from a first set of filter taps of the adaptive filter with outputs from a second set of filter taps of the adaptive filter.

### Claim 4 (depends on 3)

The method of claim 3, wherein the step of detecting convergence of the adaptive filter comprises determining a flatness of the ratio.

### Claim 5 (depends on 1)

The method of claim 1, wherein the step of determining the echo-to-disturbance energy ratio comprises:
determining an energy of the microphone input signal; and
determining an energy of the echo-cancelled output signal.

### Claim 6 (depends on 1)

The method of claim 1, wherein the step of adjusting the step size is based, at least in part, on a desired echo reduction level.

### Claim 7 (depends on 1)

The method of claim 1, wherein the step of generating the echo-cancelled output signal is performed without double-talk detection.

### Claim 8 (depends on 1)

The method of claim 1, wherein the step of adjusting the step size comprises adjusting the step size in proportion to the echo-to-disturbance energy ratio.

### Claim 9

An apparatus, comprising:
an audio controller configured to perform steps comprising:
generating an echo-cancelled output signal from a microphone input signal and a transducer output signal, wherein the echo-cancelled output signal is generated using an adaptive filter;
determining an echo-to-disturbance energy ratio by comparing an energy of the microphone input signal and an energy of the echo-cancelled output signal; and
adjusting a step size of the adaptive filter used to converge on the echo-cancelled output signal based, at least in part, on the echo-to-disturbance energy ratio, wherein the step size is an echo-signal-to-noise-ratio (ESNR)-based variable step size (EVSS) μESNR computed according to:
μ
EVSS
=
μ
⁡
(
P
in
-
P
out
)
P
in
+
(
R
-
1
)
⁢
P
out
.

### Claim 10 (depends on 9)

The apparatus of claim 9, wherein the audio controller is further configured to perform steps comprising:
detecting convergence of the adaptive filter; and
performing the step of adjusting the step size based on a convergence state of the adaptive filter.

### Claim 11 (depends on 10)

The apparatus of claim 10, wherein the audio controller is configured to detect convergence of the adaptive filter by comparing a ratio of outputs from a first set of filter taps of the adaptive filter with outputs from a second set of filter taps of the adaptive filter.

### Claim 12 (depends on 11)

The apparatus of claim 11, wherein the audio controller is configured to detect convergence of the adaptive filter by determining a flatness of the ratio.

### Claim 13 (depends on 9)

The apparatus of claim 9, wherein the audio controller is configured to determine the echo-to-disturbance energy ratio by:
determining an energy of the microphone input signal; and
determining an energy of the echo-cancelled output signal.

### Claim 14 (depends on 9)

The apparatus of claim 9, wherein the audio controller is configured to adjust the step size is based, at least in part, on a desired echo reduction level.

### Claim 15 (depends on 9)

The apparatus of claim 9, wherein the audio controller is configured to generate the echo-cancelled output signal without a double-talk detector.

### Claim 16 (depends on 9)

The apparatus of claim 9, wherein the audio controller is configured to adjust the step size by adjusting the step size in proportion to the echo-to-disturbance energy ratio.

### Claim 17

An acoustic echo cancellation (AEC) system, comprising:
an adaptive filter configured to modify an input microphone signal based on a plurality of filter coefficients to obtain an echo-cancelled output signal;
a step size controller coupled to the adaptive filter and configured to adjust an adaptation rate of the adaptive filter based, at least in part, on an echo-to-disturbance energy ratio computed from the input microphone signal, the echo-cancelled output signal, and a desired echo reduction level, wherein the adaptation rate is based on a step size that is an echo-signal-to-noise-ratio (ESNR)-based variable step size (EVSS) μESNR computed according to:
μ
EVSS
=
μ
⁡
(
P
in
-
P
out
)
P
in
+
(
R
-
1
)
⁢
P
out
.

### Claim 18 (depends on 17)

The acoustic echo cancellation (AEC) system of claim 17, wherein the step size controller is configured to adjust the step size by adjusting the step size in proportion to the echo-to-disturbance energy ratio.

### Claim 19 (depends on 17)

The acoustic echo cancellation (AEC) system of claim 17, further comprising a convergence detector coupled to the adaptive filter and coupled to the step size controller, wherein the step size controller is configured to disable adjusting of the adaptation rate of the adaptive filter when the convergence detector determines the adaptive filter is not converged.

### Claim 20 (depends on 19)

The acoustic echo cancellation (AEC) system of claim 19, wherein the convergence detector is coupled to outputs of a plurality of filter taps of the adaptive filter, and wherein the convergence detector determines the adaptive filter is not converged by comparing a ratio of outputs from a first set of the plurality of filter taps with outputs from a second set of the plurality of filter taps of the adaptive filter.