[vorbis-dev] Different floor, quality improvement

Segher Boessenkool segher at wanadoo.nl
Sat Dec 23 15:42:00 PST 2000

Some additional notes... Has anyone tried it yet?

Segher Boessenkool wrote:
> Hello all,
> Please try this "patch". It changes the way the noise floor is used
> for quantization in a not-so-subtle way.
> At the very end of _vp_compute_mask, add the lines:
>         for(i=0;i<n;i++)
>                 flr[i]=.01f*sqrt(flr[i]);
> The .01 is there to ensure the current codebooks will work. We will
> really need different, newly-trained codebooks with this change; then
> the .01 can probably go away, though it won't hurt (I think).
> Be warned that the bitstreams increase roughly 50% in size with this
> change, so you should compare 128kbps new with 192kbps old etc.

Using .028 instead of .01, you will get bitstreams of the designed bitrate.

> Please try this on tracks you find difficult to encode, especially
> very tonal stuff,
> I'll explain later what this really does, it's a bunch of math so
> I'll make a TeX file of it,

Some really inexact and quick answer:

It makes it easier on the vector quantizer to make a "fair" decision.
Now define "fair" ;-)  (In this case: "statistically fair". Now define
"statistically fair"... )

Merry Christmas to all of you, see you guys in the next millenium,


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