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From: sjc@mips.UUCP
Newsgroups: net.audio
Subject: Re: Never before asked questions regarding CD Players.
Message-ID: <566@mips.UUCP>
Date: Sun, 20-Jul-86 18:25:59 EDT
Article-I.D.: mips.566
Posted: Sun Jul 20 18:25:59 1986
Date-Received: Mon, 21-Jul-86 02:55:38 EDT
References: <885@ucbcad.BERKELEY.EDU>
Distribution: na
Organization: MIPS Computer Systems, Sunnyvale, CA
Lines: 37

> I understand that, when playing a VERY scratched disk, the single beam
> CD players put out less noise and fewer errors than three beam players.
> 
> I was given a demonstration to this fact(?) at a stereo shop: the
> salesperson brought forth a store demo disk with a significant amount
> of scratches...
> 
> He played it on a brand-x three beam machine and the noise and
> errors where definately audible.  He then proceeded to give the disk a
> run on a single beam Sony (he said all Sony machines are single beam
> due to this advantage) and the noise was either inaudible or
> significantly less than the aforementioned three beam machine.

Whether he realized it or not, your salesperson was performing a
scientific experiment, constraining one variable (the demo disk) and
allowing another (the CD player) to vary. I conclude from the results
that Sony does a better job than BrandX with this disk. He concludes
that all one-beam players do a better job than all three-beam players
on all damaged disks.

Does he know that the difference between Sony and BrandX is due solely
to the number of beams, and not to differences in the error correction
algorithms in their ICs, or in their servomechanisms?  Does he know
that this damaged disk is representative of all defective disks (some
with scratched surfaces, and others with pressing defects below the
surface?

For what it's worth, my experience with (admittedly only) a handful of
defective disks and a handful of players is that often one disk will
suggest player A is better than player B, and another disk will suggest
the opposite.  I'm glad to see that the one-beam people are fighting
back against the three-beam people, however.  For a time, I thought the
advertising copywriters were about to establish the superiority of
three beams based merely on the well-known fact that three is a larger
number than one.
-- 
...decwrl!mips!sjc						Steve Correll