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

[David Willmore]

I'm running a:
for band in n w u
  do
    for quality in 0 1 2 3 4 5 6 7 8 9 10
      do
        for complexity in 3
          do
            for vad in "" "--vad"
              do
                for dtx in "" "--dtx"
                  do
                    echo speexenc -${band} --quality ${quality} --comp ${complexity} ${vad} ${dtx} input.${band}.wav output.${band}.${quality}.${complexity}.${vad%%--}.${dtx%%--}.speex
                    /usr/bin/time speexenc -${band} --quality ${quality} --comp ${complexity} ${vad} ${dtx} input.${band}.wav output.${band}.${quality}.${complexity}.${vad%%--}.${dtx%%--}.speex
                  done
              done
          done
      done
  done

on a set of .wav files generated from ripping a CD (Doug Stanhope/Die Laughing)
which is all talk with some applause (sorry Doug).  I sox'd them down to 8k,
16k, and 32k so that speex would have something good to chomp on.

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.

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?

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
2) --bitrate  (CBR?)
3) --bitrate with --vbr
4) --abr

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. :)

Oh, please, no comments on my shell script. :)  Yes, I mean ##, not %%, but you
try to remember the difference at 2am. ;)

Cheers,
David

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