# US 6,724,899 B1 · Sound pick-up and reproduction system for reducing an echo resulting from acoustic coupling between a sound pick-up and a sound reproduction device

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- Number: US 6,724,899 B1
- Document ID: US6724899B1
- Status: Granted
- Kind: B1
- Application number: 09/429,366
- Filed: 1999-10-28
- Granted: 2004-04-20
- Earliest claimed: 1998-10-28
- Assignees: France Telecom
- Inventors: Wolfgang Taeger; Gregoire Le Tourneur
- Web page: https://patentgrep.com/patent/US6724899B1

## CPC

- H04M 1/6033: {for providing handsfree use or a loudspeaker mode in telephone sets (arrangements for preventing acoustic echo H04M9/08)}
- H04M: TELEPHONIC COMMUNICATION (circuits for controlling other apparatus via a telephone cable and not involving telephone switching apparatus G08)

## Abstract

A sound pick-up and reproduction system includes at least two sound sensors, such as microphones, situated at different distances from a sound reproduction device, such as a loudspeaker. A processor responds to amplitudes and phases of signals outputted by the at least two sound sensors to control a signal outputted to an amplifier and adapted to drive the sound reproduction device, thereby reducing echoes in the sound reproduction device output caused by acoustic coupling between the at least two sound sensors and the sound reproduction device.

## Claims

### Claim 1

A system of reducing echoes resulting from acoustic coupling, the system comprising:
a sound pick-up device having a signal output;
a sound reproduction device;
an application unit having an input connected to said signal output of said sound pickup device and having an output connected to an input of said sound reproduction device, said sound reproduction device adapted to reproduce said signal output from said sound pick-up device;
said sound pick-up device including at least two sound sensors situated at different distances from said sound reproduction device and further including a processing unit adapted to process signals outputted from said at least two sound sensors and to output said sound pick-up device signal output to said application unit, said processing unit reducing an echoes in said sound pick-up device signal output caused by acoustic coupling between said sound pickup device and said sound reproduction device;
said processing unit including a filter adapted to filter an output signal from each of said at least two sound sensors and a summer adapted to sum a filtered output signal from each of said at least two sound sensors;
wherein each filter of said processing unit has a pulse response defined by a function gi(t) that is a solution calculated once and for all of the following equation: ∑ i ⁢ ⁢ [ h i ⁢ ⁢ ( t ) * g i ⁢ ⁢ ( t ) ] ≈ 0
for i varying from 1 to n, wherein n is a positive integer equal to the number of sensors; and
wherein hi(t) is a previously obtained impulse response of each of said at least two sensors to signals outputted by said reproduction device is for i varying from 1 to n, and wherein* represents a convolution operation.

### Claim 2 (depends on 1)

The system of claim 1, wherein each function gi(t) is determined by solving said equation with an adaptive algorithm.

### Claim 3 (depends on 1)

The system of claim 1, wherein each function gi(t) is determined by solving said equation with a mean square algorithm.

### Claim 4 (depends on 1)

The system of claim 1, wherein said pulse response of each of said plurality of sound sensors to said signals outputted by said sound reproduction device is determined by measuring a response of each of said plurality of sound sensors to said signals outputted by said sound reproduction device.

### Claim 5 (depends on 1)

The system of claim 1, wherein said filtering of said output signal from a sound sensor disposed further away from said sound reproduction device than any other of said at least two sound sensors is defined by a multiplication function.