[vorbis] what is floor? HERE IT COMES :-)

[Vincent]

thanks to all the people who answered.

There is still something that i don't understand :
The floor is an approximation of the spectral image of a chanel, and the
residue is the real spectrum of the chanel minus the floor.
Then only the residue is encoded ?
If so, when decoding, how the decoder can know the shape of the floor that
has been used to obtain the residue?
If not, both the floor and the residue are encoded, then it means it takes
the same space than encoding the real spectrum, isn't it?

<p><p>----- Original Message -----
From: "Sebastian Gesemann" <sgeseman at upb.de>
To: <vorbis at xiph.org>
Sent: Sunday, October 05, 2003 2:49 PM
Subject: Re: [vorbis] what is floor? HERE IT COMES :-)

<p>> On Fri, 3 Oct 2003, Giuliano Pochini wrote:
>
> > I may be wrong, but the floor is a smoothed version of the frequency
> > spectrum. When you subtract it from the actual spectrum you get a
> > quite flat spectrum, a sort of white noise. It still contains a lot
> > of information that has to be saved in order to be able to eventually
> > recreate the original sound.
>
> The semantics of floor curves depends on the strategy of
> the used encoder.
> It is ACTUALLY used (current libVorbis) as a smooth
> quantization curve much like the quantization matrix in
> JPG/MPG.
>
> Anyway, it's up to the encoder how to calculate
> floor & residue of each channels because there're
> more than one possible factorization of the
> specrtal vector (into flor*residue).
>
> In general, the flor-curve is a compact coded curve to
> SCALE the residue vector. (ever heard of scalefactors
> in MP3?)
>
> bye,
> Sebastian
>
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