kend@tekig.UUCP (Ken Dobyns) (06/21/84)
I have a question for the readers of this newsgroup which I hope will not rekindle some feud which has just settled down. I recently journeyed to the local high end stereo store for my first look at the CD's. After getting the necessary sales pitch extolling the virtues of the machines, including the claim that the disks were virtually indestructable, I listened to their demo mid-priced Sony. Every 10-15 seconds or so there would be a void in the music, just a brief moment of silence, almost as if the machine lost a bit of information. The salesman then proceded to blame the problem on the scratched (yet still indestructable) disk he was playing. My question is whether the problem was indeed with the disk (it really was scratched up), or if it is something inherent in the machines themselves. Thanks in advance, Ken Dobyns Tektronix, Beaverton OR
shauns@vice.UUCP (Shaun Simpkins) (06/22/84)
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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