Vorbis dev - Oct 2002 - Spectral phase information in residue vectors

I found this sentence in the Ogg format specs:
http://www.xiph.org/ogg/vorbis/doc/vorbis-spec-res.html 
"A residue vector may represent spectral lines, spectral magnitude,
spectral phase or hybrids as mixed by channel coupling."

But where does the spectral phase information come from ?
AFAIK  MDCT doesn't provide any phase information.
And in OGG-encoding, MDCT is taking place a few steps before computing
the residue vectors.

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Stoffke wrote:
> I found this sentence in the Ogg format specs:
> http://www.xiph.org/ogg/vorbis/doc/vorbis-spec-res.html
> "A residue vector may represent spectral lines, spectral magnitude, 
> spectral phase or hybrids as mixed by channel coupling."
>
> But where does the spectral phase information come from ?
> AFAIK  MDCT doesn't provide any phase information.
<p>The MDCT itself does not provide phase information, but I believe the 
spectral phase referred to here is in reference to the values stored in 
the residue after channel coupling.  It's the phase relationship between 
two values, the left and right channels, that are stored in the residue, 
if channel coupling is used.

Hope that helps,
Alan

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On Tue, Oct 22, 2002 at 10:21:43PM +0200, Stoffke wrote:
> I found this sentence in the Ogg format specs:
> http://www.xiph.org/ogg/vorbis/doc/vorbis-spec-res.html
> "A residue vector may represent spectral lines, spectral magnitude,
spectral phase or hybrids as mixed by channel coupling."
> 
> But where does the spectral phase information come from ?
> AFAIK  MDCT doesn't provide any phase information.
> And in OGG-encoding, MDCT is taking place a few steps before computing
> the residue vectors.
'phase', at least as I had intended in that example, is the elliptical
angle between two channels, phase being a synonym for angle.

Monty
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> And in OGG-encoding, MDCT is taking place a few steps before computing
> the residue vectors.
It's not a "few steps before" it; it's an integral part of it.
Don't think
in steps or stages or little black boxes; try to see it as one big thing:
mdct + floors + residues + codebooks (and channel coupling is just part of
the codebooks, if you look at it sideways ;) )

<p>Segher

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