Noise Cancellation; Automatic Gain Control (Agc) - Polycom SoundStructure C16 Design Manual

Design Guide for the Polycom SoundStructure C16, C12, C8, and SR12
Phone In
Channel
To Telco
from Matrix
From Telco
to Matrix

Noise Cancellation

Automatic Gain Control (AGC)

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.
Telephony Processing
Dynamnics Parametric
Processing Equalization
Tone
Generator
Parametric Dynamics
Delay Fader
Equalization Processing
level_post
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 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
level_post
D/A
Delay Fader
Converter
Line Echo
Cancellation
Automatic Noise A/D
Gain Control Cancellation Converter
Call Progress
Detection
level_pre
Phone Out
Channel
Output to
Analog
PSTN Line
Gain
Input from
Analog
PSTN Line
Gain