>
> > how about altering some of the mp3 specs themselves and creating a lame
> > specific mp3 variant?
> > are there any legal reasons not to do this? would the quality gain be
> > worth the effort?
>
> The problem is that no player would them be able to play the files. MP3 is
> an internationnal standard, and I think that we must follow it.
> For creating a new standard, there is another project called Vorbis.
>
>
There is one thing I would like to do, but the work in LAME
seems to never end :-) A variant on MP3 which
uses everything from LAME, but with the following changes:
1. go to transform sizes 1024 and 128
2. replace polyphase fitlerbank + MDCT with one large MDCT
3. allow mid/side stereo to be turned on/off for each critical band.
This would be a new standard, but it could only be an improvement over
the current LAME/MP3.
Vorbis is a very different codec, so it might be might be good to have
both a VQ codec (Vorbis) and a traditional scalefactor/critical band
codec.
Vorbis uses vector quantization which combines entropy coding and
quantization in one step. The quantization error is controlled by the
choice of codebook (fixed in advance?) and to a lesser extent by the
choise of the "floor" function which is derived from the psycho
acoustics. But Vorbis is unusual in that, IIRC, the encoder does not make
these choices based on the quantization error for the frame being
encoded.
MPEG on the other hand spends a lot of effort (maybe even too much
effort?) on "noise shaping". Via scalefactors, it adjusts the
quantization accuracy by looking at the quantization error and
comparing it to the psycho acoustic masking. Then the quantized
coefficients are huffman coded in a seperate, lossless step.
LAME's VBR modes take this approach to the extreme :-)
Vorbis is also VBR, but bitrate is not chosen to achieve
a quantization error < psycho acoustic masking,
so Vorbis VBR is more similar to LAME's ABR mode.
Mark
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