Polycom SoundStructure C16 Design Manual page 509

Mute all the microphones except for one and on the unmuted microphone, check the value of the AEC
reference. In the following figure the AEC reference is set to the "Amplifier" stereo virtual channel.
Next, check the matrix to ensure the "Amplifier" virtual channel includes the remote audio sources. An
example of the "Amplifier" channel and all the remote audio sources that make up the "Amplifier" channel is
shown in the following figure. Notice that the audio from the Polycom Video Codec, the telco audio, the
program audio, and the audio from the remaining remote source are all part of the "Amplifier" virtual channel
and consequently used as the AEC reference.
If the AEC reference does not include a particular remote audio source, then whenever that remote audio
source is active, there will be residual echo sent back to that remote source. For example, if the telephone
signal is not part of the reference, then when the telephone participants speak, they will hear an echo of their
voice being sent back to themselves.
If the reference is set properly, and the reference is configured properly in the matrix, the next step is to
check the room gain of the system and make sure it is not too high. Installing SoundStructure Devices
discusses acceptable room gain levels, and how to reduce room gain by lowering the audio amplifier level
and increasing the input gain on the remote audio coming into the SoundStructure to ensure the signal
levels are at a reasonable level.
Polycom, Inc. 509