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Voice Activity Detection
  
Apr 16, 2009
The concept of VAD is widely accepted after ITU G.729B and G.723.1 included it as part of the voice encode and decode algorithm. Cisco had used the idea a little earlier before the G.729B standard. In Cisco systems, voice is first sent to a pre-process VAD system before passing to standard voice codec like G.711 and G.729. The open source Speex works in the Cisco way, its VAD part is actually independent of Speex codec itself.
Now it is more than 13 years after the publish of G.729B and G.723.1. We gradually find that VAD is less and less useful in today's IP phone. We do not need it to save bandwidth any more. And we care much less of the power consumption it can possibly save too. Instead, none codec related VAD algorithm can always have bad effect on voice quality and network jitter buffer handling. There is no reason to keep a VAD option in the phone if G.723.1 and G.729B is not used.
Actually we are not alone. GIPS has not included a VAD part in its open source iLBC internet voice codec. And VAD is also not a part in GIPS' VoiceEngine product neither. What important today is AGC, AEC and PLC with dynamic jitter buffer handling.

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