Chapter 15 - Voice Transmissions
Voice Activity Detection
242
Mediatrix 4104
Voice Activity Detection
The Voice Activity Detection (VAD) defines how the Mediatrix 4104 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.
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 4104 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.
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 156:
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.
Summary of Contents for Mediatrix 4104
Page 23: ...Installation and Web Page Configuration ...
Page 24: ...Page Left Intentionally Blank ...
Page 136: ...Chapter 5 Web Interface Telephony Miscellaneous 114 Mediatrix 4104 ...
Page 144: ...Chapter 6 Web Interface Advanced STUN Configuration 122 Mediatrix 4104 ...
Page 145: ...SNMP Configuration ...
Page 146: ...Page Left Intentionally Blank ...
Page 184: ...Chapter 8 IP Address and Network Configuration Ethernet Connection Speed 162 Mediatrix 4104 ...
Page 196: ...Chapter 10 DNS SRV Configuration DNS SRV Oriented Settings 174 Mediatrix 4104 ...
Page 226: ...Chapter 12 Configuration File Download Configuration File Example 204 Mediatrix 4104 ...
Page 242: ...Chapter 13 Software Download Emergency Software Procedure 220 Mediatrix 4104 ...
Page 268: ...Chapter 15 Voice Transmissions User Gain 246 Mediatrix 4104 ...
Page 278: ...Chapter 17 Bypass Configuration Bypass Connector Settings 256 Mediatrix 4104 ...
Page 322: ...Chapter 21 Digit Maps Digit Map Examples 300 Mediatrix 4104 ...
Page 350: ...Chapter 24 Telephony Attributes Call Rejection 328 Mediatrix 4104 ...
Page 362: ...Chapter 27 Quality of Service QoS VLAN 340 Mediatrix 4104 ...
Page 366: ...Chapter 28 Syslog Daemon Syslog Daemon Configuration 344 Mediatrix 4104 ...
Page 370: ...Chapter 29 Statistics RTP Statistics 348 Mediatrix 4104 ...
Page 385: ...Appendices ...
Page 386: ...Page Left Intentionally Blank ...
Page 400: ...Appendix B Standard Hardware Information Warranty 378 Mediatrix 4104 ...
Page 404: ...Appendix C Cabling Considerations RJ 11 Telephone Cable 382 Mediatrix 4104 ...
Page 446: ...Appendix E Glossary Wide Area Network WAN 424 Mediatrix 4104 ...