[vorbis] Models used in mp3 and Ogg Vorbis?

[Jack Moffitt]

> MP3 and Ogg Vorbis use different models in order to remove most of the bits.
> What is the names of these models and how do they differ?

The models are generally similar and their basic properties have been
known for a long time.

What's really different is the implementation of these models within
each codec.

Vorbis uses vector quantization in order to store the data of the model.
It has other fancy tricks up its sleeve as well.  It also has a large
amount of basic improvements over ways of doing things in MP3 (example:
MP3 splits data into subbands with a lossy transform, them does more
transforms on those.  Vorbis just does one big lossless transform).

MP3 uses subbanding, different kinds of transforms, and different kinds
of data representation.

The properties of sound that allow it to by compressed well lossily are
the same for both codecs.  Both use the same basic ideas to take a whole
lot of sound, and turn it into a little bit of sound that is perceived
as the same by human ears.  While Vorbis probably has many improvements
in this model over other codecs (although I suppose it's possible for
those codecs to borrow these back from us), the real hard work comes in
representing the information in the most compact way possible.  Various
representations have their plusses and minuses.

In essence, MP3 is quite old technology-wise.  Vorbis is fairly young.
We have solved the same problem with novel and modern methods.  You can
think of it like MP3 being the geocentric model of the universe, and
Vorbis being heliocentric.  Both models predict the positions of astral
bodies, but one is more modern and more accurate than the other :)

(For more information, visit mp3tech.org and read a little about how MP3
works and it's basic algorithm diagram.  Then perhaps read some on
vector quantization.  If you're more interested in the psycoacoustics,
they are basically the same for Vorbis and MP3 I think, although I'd
make the case that Vorbis is much finer tuned :)

jack.
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