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From: sjc@mips.UUCP (Steve Correll)
Newsgroups: net.audio
Subject: Re: advice on CD players
Message-ID: <404@mips.UUCP>
Date: Tue, 18-Mar-86 13:23:23 EST
Article-I.D.: mips.404
Posted: Tue Mar 18 13:23:23 1986
Date-Received: Fri, 21-Mar-86 20:40:53 EST
References: <817@alberta.UUCP> <253@catnip.UUCP> <601@mmm.UUCP> <264@catnip.UUCP>
Distribution: na
Organization: MIPS Computer Systems, Sunnyvale, CA
Lines: 22

> > This statement, while possibly true in specific comparisons, is not
> > true in the general case.  A while back, reviewers were finding that
> > certain Philips single-beam players would out-track certain Japanese
> > three-beam players on defective discs.
> 
> By eccentric discs, I mean those with the hole punched off-center, not
> with other types of defects.  According to the service technician I spoke
> with at Studer/Revox (a company that makes single beam units), the
> configuration of the three beam machines is much more resistant to this
> type of mistracking.

Why are they more resistant to eccentricity? As I said in an earlier
posting, the original Philips Technical Review papers explain that
their single-beam mechanism shines one beam onto four detectors, and
uses the imbalance between the detectors to the right of the track and
those to the left of it to generate a correction signal that servos the
optical mechanism.  This is quite similar to Mr. Broder's description
of the three-beam mechanism. Can somebody explain why one wide beam
impinging on four detectors is inferior to three beams impinging on
three detectors?
-- 
...decwrl!mips!sjc						Steve Correll