[vorbis] Lossy Audio Compression Research

[Maik Merten]

Ross Vandegrift schrieb:
> 
> Hello everyone,
 
Hello Ross!

>         I'm a student at the Universtiy of Delaware, and will be soon starting
> some research on the effects of lossy audio compression on speech sounds.  I
> will be preforming test with both mp3 and vorbis.
 
Sounds interesting. Oh... by the way - isn´t Gian-Carlo Pascutto working
on a speech-optimized tuning of the encoder?

>         First of all, if I use the '--ogg' switch to lame, does lame use GPSYCHO
> to encode the wave, or some other psychoacoustic model (perhaps one designed for
> the vorbis algorith)?  Along these lines, I'm unable to get lame-3.89 and
> libvorbis rc2 to play nicely together.  The lame build breaks when compiling
> ogg support (this is probably a known bug, so I'm not posting relevant details.
> If I'm wrong about it being know, we'll go from there).
 
Long, long ago (your grandparents may remember their grandparents
knew about it... ;-) you could compile Vorbis support into
lame. Due to API-changes this isn´t possible anymore - and the
lame guys don´t seem to be interested in updating their
Vorbis-interface.

But this isn´t as bad as it sounds: Lame´s Vorbis-output was
_exactly_ the same as oggenc´s output. Lame simply used the
routines of libvorbis - so does oggenc.

The "--ogg" switch never influenced MP3-Output and it never
will. AFAIK the MP3-psychoacoustic model is somewhat different
from the Vorbis one - you can´t exchange them.

>         Second, since audio compression is based on the idea of a plausable
> psychoacoutic model.  There seems to be some documentation on GPSYCHO, which
> lame uses.  But the link 'The Vorbis probability model' on xiph.org is noteably
> not a link.  Is there any addition documentation about the psychoacoustic model
> that vorbis uses?
 
I´m neither a developer nor involved in documentation. Hmmm... I don´t
know where to find it.

>         Finally, does anyone know of similar studies that have already been
> performed, either academic or not?
 
I never heard of such studies. But I never searched for those studies
:-)

> Thanks,
> Ross Vandegrift
> ross at willow.seitz.com
 
Hope this was useful,

Maik Merten


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