[speex-dev] Speex Options

Jean-Marc Valin Jean-Marc.Valin at USherbrooke.ca
Wed Nov 26 15:32:47 PST 2003

> I have a few questions about which options are mutually exclusive;
> It appears that if you set ABR to a specific value, it says in speexenc
> you don't need to specifically turn on DTX, VBR or VAD, and from the
> code and documentation it appears that you don't need to set VBR
> quality or set Quality either- this should be done by the open loop algorithm.

Basically ABR implies VBR and VBR implies VAD (but no longer DTX). Also,
if you specify --vbr, you need to specify quality, but if you use --abr,
only the quality is dynamically adjusted to match the bit-rate

> Also, is the VAD in the pre-processing code different from
> the VAD that is used in the current code base?

They are very different. The VAD integrated in the encoder is very rough
and low complexity while the one in the preprocessor is done in the
frequency domain and should be much better. They don't serve exactly the
same role either. The VAD in the encoder is tuned to encode everything
but stationary noise, while the preprocessor VAD is tuned to reject
non-stationary noise too (ideally anything that's not speech). 


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

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