Polycom SoundStructure C16 Design Manual page 315

TroubleShooting
Because the AEC reference is available after the fader as presented in Chapter
3 and shown in the following figure, the result is that the AEC reference is also
attenuated and therefore the echo canceller would not be able to remove the
echo because the reference level is attenuated too much.
Output Processing
AEC
Reference
Parametric
Mute
Output from
Dynamics D/A Analog Output
or Graphic Fader Delay
Matrix
Converter Gain Signal
Processing
Equalization
The solution to this issue is to use the line output gain instead of the fader to
attenuate the signal to match it to the signal level requirements of the next
piece of equipment in the signal chain. Changing these settings are shown in
10 - 7