[vorbis] bitrate peeling

[Segher Boessenkool]

"Daniil V. Kolpakov" wrote:
> 
> On 7 îÏÑÂÒØ 2002 23:03, Christian.Buchner wrote:
> > As far as I know MP3 stores subband by subband in Huffman coding.
> > That means you can cut away whole subbands to cut off the high
> > frequencies for example. But that's about all you can do without
> > resorting to re-quantization.

Just cutting away bands gives you the famous "tin roof" tinkling sound.
Can't just cut out parts, you have to use a less steep low pass filter
-- this is MDCT, after all.  Same problem happens a *little* less
severe with Vorbis.

> That's why mpg123, Winamp and others can decode 44kHz mp3s to, say,
> 11kHz PCM with lower CPU usage.

That will give a lot of aliasing noise, then.  Bad idea (unless you
_have_ to, due to processor limits or such, of course).

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