Aec Reference; Tail Time - Polycom SoundStructure C16 Design Manual

it is possible to make the system appear more full-duplex at the expense of potentially having some residual
echo transmitted to the remote site if the acoustic echo canceller is not fully converged.
AEC
Near Out Far In
Filter
Near In
Far Out
NLP

AEC Reference

The AEC reference provides the AEC with the information of what signals it should cancel from the room
(see the following figure). The echo canceller reference is usually a combination of audio from the remote
sites including telephone and video conferencing audio and also any program audio sources. Microphone
signals are typically not included in the acoustic echo canceller reference signal.
In order to cancel echoes, the original source signal (the remote audio) must be part of the echo canceller
reference. Generally the reference is the original signal that is played out of the loudspeaker system (as
shown in the following figure) before it generates echo in the local room.
If the reference signal is significantly different from signal played out of the loudspeaker (due to dynamics
processing, for instance), the echo canceller may not be able to cancel the echo signal because it is not
recognized as being the same as the reference signal, causing a persistent residual echo to be sent to the
remote site as the local echo canceller treats this signal as a local talker. Do not apply dynamics processing
or other non-linear signal processing on the loudspeaker signal as that will distort the echo signal
substantially from the signal the echo canceller is expecting to see for the echo canceller reference. If
dynamics processing is required, process the signal before it is used as the echo canceller reference.
A
AEC
Far In
Near Out
Filter
Near In
Far Out
NLP

Tail Time

The tail time of an echo canceller is the amount of time the echo canceller can still recognize a signal as an
echo from the remote talkers' speech and not interpret that signal as speech from a local talker.
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