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Path: utzoo!decvax!decuac!cvl!jc
From: jc@cvl.UUCP (John Canning)
Newsgroups: net.audio
Subject: Print-thru: Magnetic or Mechanical
Message-ID: <937@cvl.UUCP>
Date: Thu, 7-Nov-85 11:53:24 EST
Article-I.D.: cvl.937
Posted: Thu Nov  7 11:53:24 1985
Date-Received: Fri, 8-Nov-85 01:57:05 EST
Distribution: na
Organization: Computer Vision Lab, U. of Maryland, College Park
Lines: 28

Several recent net.audio postings have talked about print-thru problems
on vinyl disks.  I've always thought that 'pre-echo' was due to the music
etched into the next groove of the record affecting the groove in which
the needle is located.  It seems unlikely to me that the very weak
permanent magnetic fields emanating from a layer of tape could affect
the adjoining tape layers on the reel.

  If it is a magnetic phenomenon, then the way in which the reel is
wound should have litte effect on the print thru because the adjoining
layers of tape have just reversed position.  The magnetic particles
are on only one side of the tape, but the distances between layers
remain the same.  Thus, depending on winding direction one would get
either pre-echo or post-echo.  Post-echo may not be as easy to detect
because the sound usually has a longer decay time than rise time and the
ear can't adjust to hear faint sounds after a loud passage.
The pre-echo time delay constant would be a function of the position on
the tape of the music since the reel diameter (and circumference) vary
with position (and change order when wound backwards).

  If it is a mechanical phenomenon, then it should be stronger in one
channel (the channel etched on the side adjoining the next groove) than
the other.  The record should also be in the same orientation at the
onset of the pre-echo and at the onset of the corresponding music.
Since I don't have any records with noticeable print-thru, I'd be interested
to hear if other people's print-thru satifies/doesn't satisfy these
conditions.

                          - John Canning (jc@cvl.umd.edu.arpa)