[vorbis] c't listening test: Ogg problem at 128kbps

[Giuliano Pochini]

> lossless-coupling will be used for -q6 .. -q10 AFAIK.
> you probably meant the point-stereo-thingie.

Yes, yes, I meant lossy, not lossless (my poor english, sorry).

> i think it's a quantizing problem.
> when quantizing a set of small values like the mdct-coeffs for high
> frequencies, the energy difference (between unquantized and quantized
> coeffs) may be much graeter than by quantizing large values.
>
> But the point-stereo mechanism seems to be a problem for me, too.
> the angle-value of the square-polar-mapped vector will always be set to
> zero which leads to a 3dB gain in worst case (worst case = phase
> difference of 90 degrees)

Yes, but I think that the effect is amplified by the brain too. In-phase
signals are perceived stronger that out-of-phase ones. This could explain
why this treble amplification can be heard mainly with headphones (or
at least I do).

> To compensate these tings, the encoder should "carefully" encode the floor
> and "carefully" quantize the coeffs according to the resulting
> energy-level.

I agree. This should also reduce the harshness caused by moving some frqs
to the center and other ones to the sides (n>1-way stereo), which get
amplified by different factors.

> i just read the vorbis-spec, but i'm not familar with the internals of the
> vorbis-codec, wether/how it takes care of...

We're all awaiting for documentation :))

<p>Bye.

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