Polycom C16 - Manual (Page 312)

Design Guide for the Polycom SoundStructure C16, C12, C8, and SR12
10 - 4
Echo Troubleshooting
Many echo problems can be traced to:
1. Check loop-back echo. A matrix cross-point may have been inadvertently
unmuted, causing a direct replica of the audio to be heard remotely.
2. AEC Reference is setup incorrectly (see chapter 5). Note: AEC reference
needs to include ALL the remote audio sources. Any remote audio that is
not part of the reference will hear echo going back to that site.
3. Room gain is too high (see chapter 7). A typical method to reduce the
room gain is to provide a better input level to the SoundStructure device
and lower the amplifier level. Others may require a different placement
of loudspeakers and microphones.
4. Audio has too much non-linear distortion. If the playback audio is
clipping the loudspeaker, the resulting echo picked up at the microphone
can also become nonlinearly distorted. In this case, the AEC will not
adapt to the room echo correctly. One way to resolve this is to lower the
amplifier level or the digital gain inside the SoundStructure of the audio
path going to the amplifier output.
The Remote People Hear Echo Of Their Voices From The Local Room
Mute the local microphones and ensure the echo is removed for the remote
participants when the local microphones are muted. Unmute the local micro-
phones and ensure the echo has returned.
If the echo is present when the microphones are unmuted and not there when
the local microphones are muted, it is likely an acoustic echo canceller config-
uration issue with the local room. If the echo is still there when the
microphones are muted, it is not an acoustic echo issue and may be an issue
with wiring or with routing through the matrix.