Hello,
After a few dozen of those frequency analysis graphs, I noticed
something that made me curious: The 16+kHz region of a VBR encoded
file vs the 256S cbr.
http://users.belgacom.net/gc247244/extra/why_oh_why.png [8KB]
is a _very_ striking illustration, and I started thinking about this.
As you can see, the shape of the curve is still there, but there is a
constant dB drop in the 16->22kHz region.
Why is this?
the best I could come up with:
- VBR: psy-model does noise calculations, decides at many instances the 16-22kHz
(background)noise is below hearing treshold, decides upon lower bitrate, and the
MDCT coefficients from high freqs, which are the least important, are
scaled: 0 bits available. => Average fft sum of decoded mp3 gives
drop in dB's. At points where needed (>treshold), the high band is represented
correctly.
- bug (aka "feature")
I'm trying to get some understanding in this matter, so please, I'd
like some educated material or guesses...
Q: Why so outspoken in the 16kHz band (32th band? [I keep hearing
"22", but prolly just 16->22 meant?]
Why no gradual decrease in db's progressive with freq, throughout
different bands?
thanks :)
--
Best regards,
Roel mailto:[EMAIL PROTECTED]
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