peeling as I understand it (was Re: [vorbis] When will quality increase be unnoticable?)

[Alan MacDonald]

> -----Original Message-----
> From: owner-vorbis at xiph.org [mailto:owner-vorbis at xiph.org]On Behalf Of
> Graham Mitchell
> Subject: peeling as I understand it (was Re: [vorbis] When will quality
> increase be unnoticable?)

> That is, if a file is encoded at (for example) q9, and subsequently
"peeled" to q6, it may not sound quite as good as the same file originally
encoded at q6.
So they'll peel, and the bitrate (and filesize) will be right
where you want it, but the quality may be sub-optimal.  But this depends
probably on how "smart" the peeler is.

<p><p><p>Well I wish someone would give a clearer explaination of what is meant by
peeling, because there are at least two ways, that I can see, to effectively
reduce the bit-rate of a vorbis file with out completely decoding then
re-encoding.  The simplest way is to drop some of the residue codes, which
would give you a sub-optimal result, as Graham mentioned.  The second is to
decode the data to right after the codebook stage and then use a new set of
codebooks (ones for a lower quality level, and re-encode) which should be,
in theory, quite effective at reproducing what a file encoded at the lower
quality rate would produce, I think...

Although this would be a little more CPU intensive, it is still much less
intensive than encoding on-the-fly because you never leave the frequency
domain.  But, I think what we are talking about is the first scenario, where
coarser values are used for the residue, because of the layered nature of
the residue quantization.  Does anyone know?

Thanks,
Alan

<p><p>--- >8 ----
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