Noise Cancellation - 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 - 64
The location of the telco signal meters are shown in the following figure. The
input channel meters level_pre meter corresponds to the meter next to the
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
Delay
Processing Equalization
Tone
Generator
Parametric Dynamics Automatic
Fader
Equalization Processing Gain Control
Call Progress
Detection
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.
level_post
D/A
Analog
Fader
Converter
Gain
Line Echo
Cancellation
Noise A/D
Analog
Cancellation Converter
Gain
level_pre
Phone Out
Channel
Output to
PSTN Line
Input from
PSTN Line