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

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.
Telco Signal Meters
Phone In
Channel
To Telco
from Matrix
From Telco
to Matrix

Processing 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 cancellation can be
adjusted from 0 to 20 dB.
The SoundStructure noise cancellation effectively removes different types of background noise ranging
from narrow band noise (tones) to broadband noise. For best performance, the noise characteristics should
be quasi-stationary, for example, the statistics of the underlying noise are fixed or change slowly over time.

Using Automatic Gain Control (AGC)

Automatic gain control is used to automatically adjust the gain of audio signals so that the average signal
level is close to the SoundStructure nominal signal level of 0 dBu. The AGC system is 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 meter and the text box next to the AGC meter.
The range of the AGC can be adjusted by expanding the AGC control and adjusting the maximum and
minimum gains. By default the maximum and minimum gain are set to 6 and -6 respectively on microphone
and telephony signals.
The maximum AGC value specifies the maximum amount of gain the AGC can apply to increase the input
signal level as the AGC tries to reach the SoundStructure nominal signal level.
Polycom, Inc.
Telephony Processing
Dynamnics Parametric
Delay
Processing Equalization
Tone
Generator
Parametric Dynamics Automatic
Fader
Equalization Processing Gain Control
Call Progress
Detection
level_post
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
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