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Path: utzoo!watmath!clyde!cbosgd!ihnp4!stolaf!umn-cs!mmm!schley
From: schley@mmm.UUCP (Steve Schley)
Newsgroups: net.audio
Subject: Re: White Noise on CD's
Message-ID: <246@mmm.UUCP>
Date: Thu, 17-Oct-85 09:27:01 EDT
Article-I.D.: mmm.246
Posted: Thu Oct 17 09:27:01 1985
Date-Received: Sat, 19-Oct-85 08:34:06 EDT
References: <148@birtch.UUCP> <193@polaris.UUCP>
Reply-To: schley@mmm.UUCP (Steve Schley)
Distribution: net
Organization: 3M Company, St. Paul, Minn.
Lines: 31

In article <193@polaris.UUCP> herbie@polaris.UUCP (Herb Chong) writes:
>In article <148@birtch.UUCP> ken@birtch.UUCP (Ken Brown x254) writes:
>>I don't know if it is true, but my roomate has informed me that the manu-
>>facturers of CD's introduce white noise (maybe pink noise) to reduce the
>>'spikes'.  CD's will produce a "stair-step" type of waveform, and the
>>white (pink) noise produces a flat line (or curve), instead of spikes.

>this is known as dithering and there are few CD players these days
>that don't use it.  the overall S/N is reduced, but the quantization 
>noise at low levels is randomized so that subharmonics of the sampling
>frequency are not audible.

To the best of my knowledge, there are few CD players that DO use
dithering at playback.  I think Ken meant that the manufacturers of the
DISCS were incorporating white noise, and some are.  Such dithering
does just what Herb claimed for it.

For those who want to know more about dither: check the last year of
issues of the Journal of the Audio Engineering Society.  Lipschitz and
Vanderkooy published a treatise on the application of dither in audio
analog-to-digital conversion.  My study of this article leads me to
think that dither is appropriate for analog-to-digital conversion, but
inappropriate for digital-to-analog conversion.  If anyone understands
these issues and would like to comment on them, I'd like to hear from
you (preferably by mail).  I'm trying to decide whether adding dither
to my CD player will likely improve its sound.

-- 
	Steve Schley

	ihnp4!mmm!schley