Medias Mediatrix 1204, Reference Manual

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Chapter 16 - Voice Transmissions Voice Activity Detection
210 Mediatrix 1204
Voice Activity Detection
The Voice Activity Detection (VAD) defines how the Mediatrix 1204 sends information pertaining to silence.
This allows the unit to detect when the user talks, thus avoiding to send silent RTP packets. This saves on
network resources. However, the VAD may affect packets that are not really silent (for instance, cut sounds
that are too low). The VAD can thus slightly affect the voice quality.
G.711 and G.726 VAD
The G.711/G.726 VAD is generic – when enabling VAD, G.711/G.726 sends speech frames only during
periods of audio activity. During silence periods, G.711/G.726 does not send speech frames, but it may send
Comfort Noise (CN) packets (payload 13) containing information about background noise.
X
To enable G.711 and G.726 VAD:
1. In the voiceIfMIB , locate the voiceIfTable group.
2. Define the sensitivity of the VAD algorithm to silence periods in the
voiceIfG711VoiceActivityDetectionEnable variable.
The following settings are available:
The difference between transparent and conservative is how “aggressive” the algorithm considers
something as an inactive voice and how “fast” it stops the voice stream. A setting of conservative is
a little bit more aggressive to react to silence compared to a setting of transparent.
The default value is conservative .
3. Restart the Mediatrix 1204 so that the changes may take effect.
G.729 VAD
G.729 has a built-in VAD in its Annex B version. It is recommended for digital simultaneous voice and data
applications and can be used in conjunction with G.729 or G.729 Annex A. A G.729 or G.729 Annex A frame
contains 10 octets, while the G.729 Annex B frame occupies 2 octets. The CN packets are sent in accordance
with annex B of G.729.
X
To enable G.729 VAD:
1. In the voiceIfMIB , locate the voiceIfTable group.
2. Define the voiceIfG729VoiceActivityDetectionEnable variable.
Note:
You cannot disable the G.723 VAD.
In the Unit Manager Network Administration Manual , refer to chapter Ports Parameters , section Port
Configuration Window .
Table 134: G.711/G.726 VAD Settings
Setting Description
Disable VAD is not used.
Transparent VAD is enabled. It has low sensitivity to silence periods.
Conservative VAD is enabled. It has normal sensitivity to silence periods.