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From: wjm@whuxk.UUCP
Newsgroups: net.audio
Subject: Re: Cassette deck cleaners - (nf)
Message-ID: <344@whuxk.UUCP>
Date: Tue, 13-Dec-83 10:54:47 EST
Article-I.D.: whuxk.344
Posted: Tue Dec 13 10:54:47 1983
Date-Received: Thu, 15-Dec-83 01:12:55 EST
References: uiucdcs.4417
Lines: 10

The purpose of cassette (or any other type of tape deck - audio or video)
demagnetizing is to remove low level magnetism that builds up on playback heads
during use - it is caused by the magnetic fields on the tape (which contain the
information).  Record and erase heads don't need to be demagnetized since the
AC bias will remove this residual magnetism, but capstans and other metal parts
in the tape path do need it.
If you do not demagnetize, the residual field will build up and erase highs
from the tape (the high frequency signals, since they take up less area on the
tape and are more susceptable to erasure by low level magnetic fields).
Bill Mitchell (whuxK!wjm)