Configuring Voice Gain (Volume) Control; Echo Cancellation - AudioCodes Mediant 3000 User Manual

15.1.1 Configuring Voice Gain (Volume) Control

The device allows you to configure the level of the received (input gain) Tel-to-IP signal
and the level of the transmitted (output gain) IP-to-Tel signal. The gain can be set between
-32 and 31 decibels (dB).
The following procedure describes how to configure gain control using the Web interface:

To configure gain control using the Web interface:
1. Open the Voice Settings page (Configuration tab > VoIP menu > Media > Voice
Settings).
Figure 15-2: Voice Volume Parameters in Voice Settings Page
2. Configure the following parameters:
•
'Voice Volume' (VoiceVolume) - Defines the voice gain control (in decibels) for IP-
to-Tel
•
'Input Gain' (InputGain) - Defines the PCM input gain control (in decibels) for Tel-
to-IP
3. Click Submit.

15.1.2 Echo Cancellation

The device supports adaptive linear (line) echo cancellation according to G.168-2002.
Echo cancellation is a mechanism that removes echo from the voice channel. Echoes are
reflections of the transmitted signal.
In this line echo, echoes are generated when two-wire telephone circuits (carrying both
transmitted and received signals on the same wire pair) are converted to a four-wire circuit.
Echoes are reflections of the transmitted signal, which result from impedance mismatch in
the hybrid (bi-directional 2-wire to 4-wire converting device).
An estimated echo signal is built by feeding the decoder output signal to an RLS-like
adaptive filter, which adapts itself to the characteristics of the echo path. The 'estimated
echo signal' (the output of this filter) is then subtracted from the input signal (which is the
sum of the desired input signal and the undesired echo) to provide a clean signal. To
suppress the remaining residual echo, a Non Linear Processor (NLP) is used, as well as a
double-talk (two people speak at the same time) detector that prevents false adaptation
during near-end speech.
The device also supports acoustic echo cancellation for SBC calls. These echoes are
composed of undesirable acoustical reflections (non-linear) of the received signal (i.e., from
the speaker) which find their way from multiple reflections such as walls and windows into
the transmitted signal (i.e., microphone). Therefore, the party at the far end hears his / her
echo. The device removes these echoes and sends only the near-end's desired speech
signal to the network (i.e., to the far-end party). The echo is composed of a linear part and
a nonlinear part. However, in the Acoustic Echo Canceler, a substantial part of the echo is
non-linear echo. To support this feature, the Forced Transcoding feature must be enabled
so that the device uses DSPs.
The following procedure describes how to configure echo cancellation using the Web
interface:

To configure echo cancellation using the Web interface:
1. Configure line echo cancellation:
User's Manual 178
Mediant 3000
Document #: LTRT-89738