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Acoustic Echo Canceller White Paper

Acoustic Echo Canceller

White Paper

June 2011

1. Introduction

Acoustic Echo

Communication technology has advanced to the point

where teleconferences that use communication lines to

connect remote conference rooms are taking place every

day.

Fig.1 Teleconference

In a teleconference, as in

Fig.1, sound is exchanged in both

directions through communication lines. When the voice of

the person speaking in room A is transferred to room B

through communication lines and reproduced by a

loudspeaker, that voice can be heard in room B. However

the microphone in room B also picks up the voice of the

person speaking in room A and sends that voice back to

room A. Because of this, in room A, the voice of the person

speaking is reproduced by the loudspeaker as an echo. This

is referred to as acoustic echo. In addition to hindering

conversation, it can cause feedback. To have a smooth

conference, it is necessary to reliably suppress acoustic

echo.

Acoustic Echo Canceller

One way to suppress acoustic echo is, for example, to

reduce the signal level of the microphone in room B when

a person is speaking in room A. This is referred to as echo

suppression. However, when echo suppression is used and

people in room A and room B talk at the same time (double

talk), their voices get cut off. This makes it difficult for

people to hear what was said and prevents smooth

conversation. To solve this problem, in 1966, M. M.

Sondhi

[1][2] proposed an acoustic echo canceller with an

ADF (adaptive digital filter). However, to actually create

an acoustic echo canceller with an ADF, one would need

highly advanced signal processing technology and a signal

Summary of content (4 pages)

PAGE 1
Acoustic Echo Canceller White Paper Acoustic Echo Canceller White Paper June 2011 1. Introduction room A. Because of this, in room A, the voice of the person Acoustic Echo speaking is reproduced by the loudspeaker as an echo. This Communication technology has advanced to the point is referred to as acoustic echo. In addition to hindering where teleconferences that use communication lines to conversation, it can cause feedback.
PAGE 2
Acoustic Echo Canceller White Paper processing device with high computational capabilities. In 3. Implementation recent years, the advancement of signal processing In an actual teleconference, the microphone signal doesn't technology and DSPs (digital signal processors) has made just include acoustic echo; it also includes external noise d [n] , which includes background noise and the sound of it possible to create sophisticated echo cancellers. the near-end speaker.
PAGE 3
Acoustic Echo Canceller White Paper 4. Specification suppression be not less than 35 dB, but regardless of the amount of ERL, a high amount of echo suppression, approximately 70 dB, is achieved. It is clear that the acoustic echo canceller can reliably remove acoustic echo. 4.1. Measurement We evaluated the acoustic echo canceller implemented in chapter 3 in a conference room with a maximum capacity of 180 people and a reverberation time of approximately 1.0 s (Fig.5).
PAGE 4
Acoustic Echo Canceller White Paper -1.2 dB), if AEC is set to a value not greater than 2, the influence to the near-end speaker is reduced, and conversations can be conducted smoothly. The results of the performance evaluation for double talk show us that when ERL is small (the amount of acoustic echo is high), there is a tradeoff between the amount of echo suppression and the sound quality.