[vorbis-dev] Thought for the new year

Frank Klemm pfk at fuchs.offl.uni-jena.de
Wed Dec 27 14:41:19 PST 2000

::  On Wed, Dec 27, 2000 at 04:41:55AM +0100, Segher Boessenkool wrote:
::  > 1) MDCT is good for image coding
::  > 2) image coding and audio coding are two very different things
::  > 3) combine 1 and 2
::  It follows that MDCT is good for many differnt tasks.

::  > 4) if a psycho model is good, after leaving out what it tells you
::  >    you can without hurting quality, applying the same model should
::  >    yield the same results as you got before
::  > 5) from 4: decode -> encode -> decode should result in (almost) the
::  >    same stream.
::  Only if the system is stable. With most MP3 encoders, the stupid subbanded bit
::  allocation routiene is greatly affected by the quantization noise from prior
::  encoding runs. Also, things like the mid-side selection may be triggered by
::  quantization noise.
::  A while back, I did some testing and found Vorbis to be fairly stable
::  through multiple encode iterations, more so then the mp3 encoders I tested.
::  I suspect that current and future fine tuning of things like block switching
::  might, however, make the encoder less stable in this regard.
::  Whats more intresting is that the framing used in vorbis will allow many
::  types of editing without a complete decode/recode cycle.

You are right MP3 encoding is *highly* unstable. Also at very high bitrates.
3 coding and recodings and 192 kbps are enough to get pure trash. At 320
kbps you need 6 codings and recodings.

MP2 is much much more robust, at 320 kbps you need 50...100 decodings
and encodings to get the same trash.

The FhG encoder is a little bit more robust, but have a level error,
so additional the recording become more and more silent.

Mit freundlichen Grüßen
Frank Klemm
eMail | pfk at uni-jena.de       home: pfk at schnecke.offl.uni-jena.de
phone | +49 (3641) 64-2721    home: +49 (3641) 390545
sMail | R.-Breitscheid-Str. 43, 07747 Jena, Germany

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