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Path: utzoo!linus!philabs!cmcl2!seismo!uwvax!geowhiz!sean
From: sean@geowhiz.UUCP (Sean Rooney)
Newsgroups: net.audio
Subject: cd players?
Message-ID: <226@geowhiz.UUCP>
Date: Tue, 13-Aug-85 11:44:18 EDT
Article-I.D.: geowhiz.226
Posted: Tue Aug 13 11:44:18 1985
Date-Received: Thu, 15-Aug-85 00:38:16 EDT
Distribution: net
Organization: UW Madison, Geology Dept.
Lines: 51

Ok, I've read enough postings about cd's without really knowing what's
going on, how about some sort of introductory, moderatly technical, 
description of cd's from one of you "experts" on the subject.

Specifically I would like to know:

1.  Are there really more than one laser in some of these things or is
    it true (as someone has said) that one laser is used and its beam is
    split (optically?).  Furthermore, what do the additional beams/lasers
    give you that you don't get with one?

2.  What is "oversampling"?  It seems that every sample on the disk
    should be read by all machines, is oversampling the re-reading of
    a single sample multiple times, perhaps to confirm it's value?
    And if that is the case, what happens to that sample in the event
    of a descrepency?

3.  "Error Correcting Code"  This is probably the most obtuse point to
    me, does "Code" imply that there is a CPU inside these things deciding
    what to do in case of a disk error?  How do different manufacturers
    ECC differ?

4.  Output filtering, digital versus analog.   I think I have a reasonable
    grasp on this section.  Personal preference seems to be the main
    discriminator since both types of filtering can do the job.

5.  Manufacturers:  Apparantly there are two designs used, Phillips and Sony,
    which are manufactured by a limited number of companys.  These companys
    products are then marketed under many names.  Could someone come up
    with a semi-comprehensive cross-reference list of who makes what
    machine behind the trim and which design they use?

6.  Moving parts:  Does the disk itself spin or does the laser beam
    move?  If the disk spins how fast does it go and how accurate need
    the motor be?  Is this a point between which one can discriminate
    a "good" cd player from a "bad" one?

I don't want to waste anyones valuable work time coming up with the answers
to my questions :-) but I've been feeling kind of foolish reading about
"Golden Shovel" awards for statements which, to tell the truth, don't
really sound that unreasonable to me.

An alternative to an introductory posting (or mailing) could be a recommendation
of a good literature source for the information.  Note, however, that I
am not an EE and therefore not prepared for any excessively technical
Journal reading.

So go ahead and educate me.

sean rooney
!seismo!uwvax!geowhiz!sean