Specifications

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CHAPTER 2: ECHO AND NOISE CANCELLATION
ECHO CANCELLATION
Acoustic echo is a significant challenge to overcome in most any teleconferencing applications. Acoustic echo can
compromise a teleconference because it impairs participants’ abilities to understand others and communicate with one
another.
Acoustic echo occurs when microphones pick up loudspeaker audio and return it to the originating
teleconference site. This echo can cause a conference participant to stop speaking while listening to the echo.
An acoustic echo canceller removes echo by sampling audio from the remote site, and preventing it from being returned
to the originating site.
For the best clarity, every site in the conference should use echo cancellation.
There are several factors that contribute to poor echo cancellation. These include:
Poor room acoustics•
High reverberation•
High noise•
Rapidly changing acoustical environment•
Wireless or other moving microphones•
Poor microphone/speaker placement•
Automatic mic mixers that are not properly configured to work with an echo canceller•
Other audio devices such as audio processors and user gain controls that change the acoustic gain to which the •
echo canceller must adapt.
Figure 2.1 shows how an echo canceller cancels echo in a room. Audio from the distant room is sampled and used as
a reference signal.
When far-end audio is picked up by the microphone (acoustic echo), the acoustic echo canceller adapts and eliminates
the echo.
Sample
Acoustic echo
Audio from
distant room
DIGITAL ECHO
CANCELLER
Microphone mixer
Echo cancelled audio
Figure 2.1