Media; Configuring Voice Settings; Configuring Voice Gain (Volume) Control; Configuring Echo Cancellation - AudioCodes Mediant 4000 SBC User Manual

User's Manual
14

Media

This section describes the media-related configuration.
14.1

Configuring Voice Settings

The section describes various voice-related configuration such as voice volume and DTMF
transport type. For a detailed description of these parameters, see ''Configuration
Parameters Reference'' on page 835.

14.1.1 Configuring Voice Gain (Volume) Control

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

14.1.2 Configuring 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
Version 7.2
Figure 14-1: Configuring Voice Volume
181
14. Media
Mediant 4000 SBC