Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Posting-Version: version B 2.10.1 6/24/83; site alice.UUCP
Path: utzoo!watmath!clyde!burl!ulysses!allegra!alice!jj
From: jj@alice.UUCP
Newsgroups: net.audio
Subject: Noise due to digital errors, error correction, etc
Message-ID: <3811@alice.UUCP>
Date: Tue, 4-Jun-85 14:06:56 EDT
Article-I.D.: alice.3811
Posted: Tue Jun  4 14:06:56 1985
Date-Received: Thu, 6-Jun-85 03:42:26 EDT
Organization: New Jersey State Farm for the Terminally Bewildered
Lines: 57

> From allegra!ulysses!mhuxr!mhuxn!charm!prk Wed Dec 31 19:00:00 1969
> 
> ...
> 1.  Good digital systems have noise levels which are much
> smaller than the least significant bit.  That's why you
> can, in principle, copy over and over without ANY degradation.
> My bet is that the signals in digital recording satisfy this
> condition by a large margin.
This point, if that's what it is, is orthogonal to the question of
degredation.  See my previous posting.
> 2.  Computer memories reserve a significant fraction of their
> space for error-correction bits.  They suffer from having
> bits shot out at random by ionizing radiation, chiefly due to
> cosmic rays and radiactive impurities in IC packages.  With
> the right error-correcting code, however, the mean time between
> uncorrectable error can be made much longer than the obsolescence
> time of the machine.  Scientific American published a nice little
> article about this within the last two years.
Precisely.
> 3.  About digital recordings:  Even though CD-player blurbs talk about
> "error-correction", I'll bet there is none -  there's no time
You're very, very wrong.  There is significant error correction power
in the simplest of the CD players.  In the most fancy ones, they
use ALL of the 80% redundancy in the stored data to fix things.
> for it.  The real issue is, if there is an incorrect bit now and then,
> could you hear it ?  NO!  A single glitch in a digital record
YES!  A single MSB inverted shows up as a gargantuan, earsplitting
!!!CLICK!!!   The fact that you never hear any CLICK's shows just
how well the error correction works. (In fact, if things are that
bad, it zeros thee sample, rather than CLICK!ing at you.)  In fact,
the MSB's are a bit more protected for exactly that reason.
> leads to white noise of very low amplitude, as I have verified by
depends on what bit you hit.
> toying with artificial data sets simulating my experimental
Um, I don't want to all you a liar, so send me mail and
let's see what's wrong with the process.  It's a standard
test that I've carried out on every form of digital coder
compressor, or direct audio that I've worked on,
 and PCM is the most sensitive of the bunch.
> data.  You can't hear it.  Think of this another way.  Suppose
> Beethoven is playing along, and then one bit gets out of place.
> This causes a click of duration 20 microsec.  How sensitive
> would you be to that?  Not very sensitive.  These glitches 
Quite sensitive.  Sorry to be so directly contradictory,
but your article exactly contradicts my experience.
> would have to be quite frequent to be annoying.  They're not -
> ...
> 
Granted that one hit of an LSB wouldn't make any difference,
still, one hit of an MSB causes quite a ruckus.  If you meant
to say that the effect after error correction was essentially
nill, that's a different story.
-- 
TEDDY BEARS HAVE LIMITED PATIENCE! THEY DO EVENTUALLY GET HUNGRY!
"Let us remember my cat, Geoffrey, ..."

(ihnp4/allegra)!alice!jj