AudioBanter.com - View Single Post - audio-cassette copy-protection?

In , on 09/22/04
at 09:53 AM, (J) said:

The library at school has several instructional audio cassettes they
lend out. Several of these tapes have become somewhat garbled, fading
in and out and echo-ing. The library staff claims that this is
because someone has attempted to copy the cassettes. I say this is
hogwash, as I am unaware of any schemes for copy-protecting audio
cassettes -especially that would destroy the source recording!

There was a proposed (to the US Congress) cassette copy protection
scheme that involved an in band signal and a cooperating recording
deck. If a tape was "marked" as protected, the recording machine would
stop recording. As one would expect, the in band marking scheme was
found to be too noticeable and the whole scheme was scrapped and the
RIAA was unhappy.

I'm an
electrical engineer and a recording hobbyist. Am I simply ignorant of
the methods? If I'm right, what is the most likely explanation for
this type of damage? Heat? Magnetic destruction? Wear?

If the tape gets too hot, print through (magnetizing adjacent layers)
increases.

If the playback machine's heads are magnetized, some of the high
frequency information on the tape can be damaged.

Heat can physically distort the tape.

A poorly wound tape pack makes edge damage more likely.

Some old tapes will exhibit oxide shedding. This can be so bad that a
"skin" will form on the playback head, act as a spacer and cause high
frequency loss. Cleaning the playback head will correct the problem for
a short while, but the skin quickly reforms. (In my experience, this
problem is more typical of reel-to-reel decks)

Some old tapes are leaching adhesive, which can cause the tape to stick
to the playback machine's guides and heads. This can cause a variety of
problems, including severe scrape flutter or so much tape friction that
the tape may stop.

Dirty playback heads can cause temporary loss of high frequency
information.

----

Examine the tape. Is it in good condition? Dirty cassette machines can
cause tape "creasing" or stretching. The damaged tape can cause a
variety of playback problems. Some or all portions of the tape could be
damaged.

Is the cassette shell in good shape? Is the pressure pad damaged or
missing? Is the playback machine in good working order?

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