[vorbis-dev] Transient coding: AAC vs. Vorbis

[Monty]

<Pine.LNX.4.44.0406111830040.15055-100000 at gorlois.cs.upb.de>
Message-ID: <20040719174213.GF20483 at xiph.org>




On Fri, Jun 11, 2004 at 07:51:04PM +0200, Sebastian Gesemann wrote:
> On Fri, 11 Jun 2004, Segher Boessenkool wrote:
>
> > Improved audio quality by experimenting?  Hey, if everyone just
> > sits back and waits for Vorbis II, it'll never be there ;-)
>
> Come on... It's not my intention to just wait. I have
> ideas and I'm willing to share'em (this is what I'm doing
> right now) ;)

I agree with Sebastian :-)

>
> As for the transform issue: Why do you think is the MDCT not
> the best transform ever invented ? Do you want frequency varying
> time/frequency resolutions ? Do you think it's worth it ?

yes and yes.  rather, I've always wanted a hybrid transform pair, one
that focuses on frequency/pitch and another that focuses on time.  The
reason being that the ear hears and processes these seperately, and
the MDCT is only well-suited to the former.

> I've experimented with a hybrid filterbank that allows frequency
> varying time resolutions and would fit into the Vorbis world.
> But it also introduces a higher encode/decode delay and a higher
> complexity. With these catches it's not suited for the goals of
> Vorbis II, I guess. :(

Maybe, maybe not.  I had looked at the problem from a standpoint of
using two transforms together rather than one that just moves the
compromise.

> > > second, the packets are still independently decodable.
> >
> > Not if they share the floor curve etc.!
>
> They don't!

They probably will in the future (meaning V-II) due to the large
coding overhead at very low bitrates.

Monty