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From: shauns@vice.UUCP (Shaun Simpkins)
Newsgroups: net.audio
Subject: Re: Question about CD's
Message-ID: <1359@vice.UUCP>
Date: Fri, 22-Jun-84 14:41:57 EDT
Article-I.D.: vice.1359
Posted: Fri Jun 22 14:41:57 1984
Date-Received: Wed, 27-Jun-84 08:59:12 EDT
Organization: Tektronix, Beaverton OR
Lines: 43

Subject: Re: Question about CD's
References: <2118@tekig.UUCP>


The answer is, it's in both!

CDs are not indestructible; just much less sensitive to surface flaws than
other media.  They are susceptible to certain types of damage, in particular
cirumferential gouging.  This orientation wipes out large blocks of data and
can cause muting.  Radial scratches are no problem; the player's error
correction circuitry can handle this type with ease.  Take a look at the care
instructions packed with every CD - they say clean the disc ONLY in a radial
direction.  Even cleaning with a tissue circumferentially can degrade the data
if you're not careful.

The plastic covering over the disc surface is used as a lens to reduce the
rather gross incident spot size to about 1-2 microns at the playing surface.
Gouges cause diffusion, defocusing, and wierd refractions of the tracking
laser beam.  In extreme cases the pickup can skip wildly about in search of
a trackable section.

Finally, manufacturers cut costs by cutting out error correction capability
and cheapening their servo tracking systems.  See for example the Audio Mag
reports on the Sears $600 player vs. everyone else's el cheapo.  The Sears
could barely track a pristine disc!  However, the latest generation of players
have much less variation in their tracking and error correction quality.

The CD medium demands a heck of a lot of its playback equipment.  Make sure
you buy a player that is up to the task.

the wandering squash,

				Shaun Simpkins

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-- 
				Shaun Simpkins

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