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Design Guide for the Polycom SoundStructure C16, C12, C8, and SR12
5 - 62
analog input gain adjustment on the telephone input virtual channel. The
input channel level_post meter corresponds to the meter next to the input
fader control. The output channel level_post meter corresponds to the meter
next to the output gain adjust.
Noise Cancellation
The noise cancellation processing is available on the telephone input signal.
The noise cancellation reduces background noise that is present in the signal
that is transmitted from the remote site. The noise cancellation functionality
can be turned on or off with the enable button. The amount of noise cancella-
tion can be adjusted from 0 to 20 dB.
The SoundStructure noise cancellation will effectively remove different types
of background noise ranging from narrow band noise (tones) to broadband
noise. For best performance, the noise characteristics should be quasi-station-
ary, for example, the statistics of the underlying noise are fixed or change
slowly over time.
Automatic Gain Control (AGC)
Automatic gain control is used to automatically adjust the gain of audio sig-
nals so that the average signal level is close to the SoundStructure nominal
signal level of 0 dBu. The AGC system has been designed to adapt the gain
only when valid speech is present.
The AGC can be turned on or off with the AGC enable button. When the AGC
is enabled, the current AGC gain (or attenuation) can be viewed from the AGC
Phone In
Channel
Phone Out
Channel
Fader
Tone
Generator
Delay
A/D
Converter
Analog
Gain
D/A
Converter
Analog
Gain
Input from
PSTN Line
Output to
PSTN Line
From Telco
to Matrix
To Telco
from Matrix
Noise
Cancellation
Parametric
Equalization
Dynamnics
Processing
FaderDelay
Line Echo
Cancellation
Call Progress
Detection
Automatic
Gain Control
Dynamics
Processing
Parametric
Equalization
Telephony Processing
level_pre
level_post
level_post