[Icecast] AACplus

[Monty]

On Fri, Feb 25, 2005 at 02:46:22PM +0100, Dennis Heerema wrote:
> Now if that is true, technically it would be possible to use the same 
> technics (SBR and PS) added on Vorbis OGG.

No, because the specific SBR extensions are part of the MPEG patent
pool.  As it is, the current/future direction of Vorbis is to move
away from a pure transform-domain encoding anyway.  SBR would still be
applicable, but some of the same mechanics would be built into the rep
model.

SBR's fundamental basis is 'each octave is closely related to the
octave below it'.  It then implements something akin to an 'exciter'
that represents most of the upper part of the spectrum as a parametric
set of harmonic duplications of the lower octaves.

The basic idea is both sound and one that's been underexploited (upper
octaves are often harmonic duplications of lower octaves).  One can
take advantage of that without using SBR, and that's the direction I'm
going.  But there's more than the harmonic structure here; if strong
tones (the harmonic structure) of the audio is subtracted out, and
you're only looking at the leftover 'noise' in time, the subband
correlation is very strong in time as well.  I don't know if
AAC(classic)'s Temporal Noise Shaping is also exploited by the SBR
extensions in any way, but I certainly plan to exploit that fact in
future Vorbis.

Monty