[vorbis] Higher mono bitrate in CVS libvorbis

[Geoff Shang]

Hi:

I have been curious as to Vorbis' performance at -q0 for some time now.
When RC3 came out, I used a track I have here and encoded it at q0 at
11.025, 16, 22.05, 32 and 44.1khz, both in stereo and in mono.  After
having heard the great sound of -q 0 in stereo, I thought I'd see what
bitrate I got with -q0 in mono.  I was disturbed to discover that the
resulting file was 9.5kbps higher than its RC3 equivalent (48.752356 vs.
39.257918).  Admittedly, it
sounded better, but so did the stereo one and -q0 in stereo was pretty much
the same size as it was in RC3.  I also notice that ogginfo says that the
nominal bitrate for -q0 in CVS is 48.001000 kb/s, whereas it gives -q0 for
RC3 as 32.007000.  The newly tuned 32khz modes give similar results to
this, compaired to the untuned modes of RC3.

My question is, is this intentional?  I would have thought that the encoder
would have tended to hang around in the range of 2/3 of the rate of stereo,
as it has done for RC3.  Just wondering if the quality settings are wrong
or whether some kind of change has been made.

Geoff.

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Geoff Shang <gshang at uq.net.au>
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