User Manual

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.
Therefore, to ensure smooth conversation, it is better to
use a configuration in which ERL is sufficiently high
(acoustic echo is low).
Fig.7 TCL
wdt
Fig.8 A
H,S,DT
5. Conclusion
The results of the evaluation show that an acoustic echo
canceller can reliably suppress echoing and enable smooth
conversation. However, during double talk, when the ERL
is low (the amount of acoustic echo is high), it is more
likely that problems will occur, such as the sound being cut
off and the sound quality changing. Therefore, one should
appropriately install microphones and loudspeakers so as to
reduce the generation of acoustic echo and then
appropriately configure the acoustic echo canceller. By
doing so, one can ensure a smooth teleconference.
6. Reference
[1] M. M. Sondhi, “Theory and Computer Simulation of
a Self-Adapting Echo Canceller”, J. Acoust. Soc. Am,
vol.40, Issue 5, p.1255, 1966.
[2] M. M. Sondhi, “An adaptive echo canceller”, Bell
System Technical Journal, vol.XLVI, no.3, pp.497–510,
March 1967.
[3] S. Haykin, “Adaptive Filter Theory”, 3rd Edition,
Prentice-Hall, 1996.
[4] ITU-T Recommendation P.501 (06/07), “Test signals
for use in telephonometry”
[5] ITU-T Recommendation G.122 (03/93), “Influence of
national systems on stability and talker echo in
international connections”
[6] ITU-T Recommendation P.1100 (10/2008),
“Narrow-band hands-free communication in motor
vehicles”
[7] ITU-T Recommendation P.341 (06/2005),
“Transmission characteristics for wideband (150-7000 Hz)
digital hands-free telephony terminals”
[8] ITU-T Recommendation P.340 (05/2000),
“Transmission characteristics and speech quality
parameters of hands-free terminals”
Sound & IT Development Division Hiraku Okumura
Sound Network Division Ryo Tanaka
Pro Audio Division Masanobu Ando
Yamaha Corporation
10-1 Nakasawa-cho, Naka-ku, Hamamatsu City,
Shizuoka Prefecture, Japan
http://proaudio.yamaha.co.jp
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