[speex-dev] rgding VAD

Jean-Marc Valin jean-marc.valin at hermes.usherb.ca
Wed Apr 16 10:06:11 PDT 2003

> If the decoder returns sample values of '0' when it detects a nonspeech
> event, the end user will be inclined think the connection is broken,
> because then also the background noise suddenly stops.
> In other speech codecs, when the VAD detects nonspeech, the decoder
> inserts 'comfort noise', so that the end user doesn't suddenly hear a
> complete silence, but rather a continuation of the background noise.

That's exactly what Speex does. If you turn on VAD only (no DTX), Speex
encodes the background noise at 2.15 kbps. If you turn DTX on too, Speex
stops transmitting when the noise is constant and the decoder keeps
generating noise using the last parameters received. As for the '0'
that's returned, it's the return value of the function, not the bits
after encoding.


Jean-Marc Valin, M.Sc.A.
LABORIUS (http://www.gel.usherb.ca/laborius)
Université de Sherbrooke, Québec, Canada

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