Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!usc!zaphod.mps.ohio-state.edu!uwm.edu!csd4.csd.uwm.edu!info-high-audio-request
From: prls!max@uwm.UUCP (Max Hauser)
Newsgroups: rec.audio.high-end
Subject: Re: data compression
Message-ID: <12229@uwm.edu>
Date: 18 May 91 14:36:08 GMT
Sender: news@uwm.edu
Lines: 46
Approved: tjk@csd4.csd.uwm.edu
Originator: tjk@csd4.csd.uwm.edu

In article <12182@uwm.edu>, sethb@fid.Morgan.COM (Seth Breidbart) wrote:
|  
|  ...   If a file is random (in the Kolmogorov/Chaitin sense), 
|  then it _cannot_ be compressed without loss of information.  ...

I completely agree with Seth in the statement above.  As this discussion
seems to have a certain vigor I feel I should also remind everyone that it
is a *very different topic* from the original subject at hand, audio data
compression, although it may appear similar.  But the character of the data
is different, the algorithms are different, and the fidelity criterion is
very different.

First, audio data are spectacularly non-"random."  Moreover, and more
importantly, it is not inherently important whether information is "lost."
Information is supposed to be lost.  (Information is lost now, with CDs,
both in the initial quantization and in the subsequent bit-error mechanisms.
Even more information is "lost" in analog recording, through different
mechanisms.)  What is important is what you can *hear*, not bits.

|  ... It's not clear whether data need be lost for real music.  Stuff
|  like 1 kHz test tones wins.  I don't care.  Complex orchestral music,
|  recorded live, with hall and audience dynamics, will lose bits.
|  I don't know if I'll be able to hear the difference, but the bit loss
|  will be there.                --  Seth      sethb@fid.morgan.com

Artificial data like sinusoids "win" in non-perceptually-based encoding
algorithms, like homomorphic and linear-predictive coding.  See my recent
posting to this newsgroup, <11823@uwm.edu>.  Such algorithms, by the way,
sound terrible even with speech and are completely unsuited to music.

But it is precisely material like "complex orchestral music ... with hall
and audience dynamics" that the perceptually-informed audio compression
methods, as in the DCC, are designed for.  (These methods in fact are
inefficient with artificial data like sinusoids).  So you see it all depends.
We are not talking about compressing some kind of "files" of the sort
familiar to software workers on the Usenet and Internet, and our fidelity
criterion has little to do with whether "bits" are lost (though that is
itself a fascinating and separate topic, which can and surely will continue
to be discussed on this newsgroup, from many perspectives, including the
Kolmogorov/Chaitin sense).  The genuine issue in audio is in fact precisely
whether you will "be able to hear the difference."  Seth mentions above
that he doesn't know.  Neither do I.

Max Hauser      {mips,philabs,pyramid}!prls!max      prls!max@mips.com

Copyright (c) 1991 by Max W. Hauser.  All rights reserved.