[vorbis-dev] Vorbis overview

[Sebastian Gesemann]

On Fri, 12 Sep 2003, Richard Felton wrote:

> I intend to finish my Vorbis document on Monday so I will leave it over the 
> weekend to see if there are any more modifications suggested. Although the 
> document will be internal I will put a copy of the final version at the 
> same address - I know firsthand how annoying it is to find loads of dead 
> links when trying to find background info on Vorbis (I know google has 
> probably already got a link to my previous posts).

Cool! But there are some things I have to mention ...

[Vorbis encode process]
- The minus within the green circle is a bit
  misleading IMO. It should be mentioned that it's
  a minus within the "logarithmic-domain".
  It's a factorization of the specral-vector into
  floor and residue, whereas the floor will be
  stored logarithmically.
  It's reversed by the dotproduct in a decoder.
  I personally really dislike the term
  "subtraction" here.
- The meaning of the floor depends on the encoder
  strategy. It is currently used as quantization
  curve (like the Q-Matrix in JPEG/MPEG), as far
  as i could discover. (current = libVorbis 1.0)

[Psychoacoustics]
- "the floor curve is a rough approximation" of what ?
  As i said, its meaning depends on the encoder
  strategy because of the fact that the factorization
  is not well-defined.
  (note: <spectral-vector> = <floor> .* <residue>)
  ( .* = dot-product )
  The floor is generally used to scale the residue
  vector (like the scalefactors of mp1/2/3,
  aac & so on)
  Otherwise there would be large demand of many
  different code books. ;)

bye,
Sebastian

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