[speex-dev] --dtx alone does nothing?

[Jean-Marc Valin]

> So far, I've noticed that --dtx alone doesn't seem to do anything, but --vad does
> and the combination --dtx with --vad does more.  The lone exception is for wide
> and ultra-wide coding at quality 0, --vad, alone, makes the file slightly larger.
> At all other sized the ordering is always: plain==--dtx, then --vad, then --vad
> with --dtx.

All you say look normal to me.

> Does that makes sense?  I would have thought that --dtx alone would have doen it,
> but maybe it needs perfect digital silence to work?  Or only uses the voice activation
> to know when there's silence?

DTX requires the VAD to know when there's silence, so it can't do
anything without --vad. I'll add a warning for that. 

> Another point I'd just like clarified is how to specify bit rates.  There seem to be 
> four different ways to do it:
> 
> 1) --quality

Note that in narrowband mode, there are less than 11 different modes, so
quality 1 and 2 are the same, the same for 3 and 4, 5 and 6, and 7 and
8.

> 2) --bitrate  (CBR?)

yes, --bitrate is for CBR. Note there are only a few bit-rates available
so the one chosen is the first mode with a bit-rate less or equal the
the bit-rate specified.

> 3) --bitrate with --vbr

With --vbr, you control the bit-rate with --quality (which is a float in
vbr mode, but an int otherwise).

> 4) --abr

This is how can specify a bit-rate in vbr mode (no need to have --vbr
too).

> Is that right?  Can someone point me to a description of what to expect from each
> of them?  Any chance of geting a histogram output like LAME has for it's variable
> bit rate encoding?  Heck, I'd be willing to code it. :)

That would be welcome. There could be a --histo switch or something like
that.

        Jean-Marc


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

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