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Re: [ARSCLIST] Video degeneration
If the exact same tape is used for audio, video and data (which some tapes
are); the decay factors are the same except where they interface with the
playback machinery. For example, some tapes are used for linear audio
recording or helical video recording depending on the desired application.
The practical effects of tape degradation can be very different depending on
whether the read/write heads are impacting the tape longitudinally (analog
audio), at right angles (Quad video) or at a pitched angle (helical video).
There are also a number of different chemical compositions of magnetic tape.
Most current analog audio and early video tape used PET as the base polymer.
Many newer video tapes now use PEN as the polymer for the base layer. PEN
is stronger than PET but is more subject to heat effects. Early audio tapes
also used acetate for the base layer. While the polyester binders of most
tapes can be "baked" to cross-link the polymers (reduce "sticky shed"-
binder hydrolysis), if you bake a tape with an acetate base you will destroy
it. Lord only knows what would happen if you "baked" an early, paper-based
audio tape- I don't know anyone who has tried.
In the recording layer, beside the polymers, you also have a number of other
ingredients. These include, among other things, recording pigments,
lubricants and abrasives. These ingredients will be different depending on
the intended use of the tape. Analog audio tape generally uses ferric oxide
recording pigments. Some newer video tapes use active metal particles.
These particles react very differently to environmentally induced decay.
The amount and type of lubricant and abrasive in the tapes will also vary
depending on the type of head assembly it is intended to run on. As a
practical example, you can run a helical video tape that has serious
lubricant loss without noticeable problems (once or twice) while the same
degree of lubricant loss would introduce serious problems in analog audio
So, in general, you are right, magnetic tape tends to decay in similar
fashion whether it is audio, video or data tape. But, heat that can destroy
one type of tape can be beneficial to another type, lubricant loss that
makes one type of tape unusable has little short-term effect on others,
types of abrasives in some tapes can damage heads in machinery designed for
other tapes and minor stretching or damage that would go unnoticed on some
tapes can cause major loss of tracking or signal on others . The issues are
similar but the effects and restoration requirements can be very different.
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> -----Original Message-----
> From: Association for Recorded Sound Discussion List
> [mailto:ARSCLIST@xxxxxxx]On Behalf Of Brandon Burke
> Sent: Thursday, December 11, 2003 12:46 PM
> To: ARSCLIST@xxxxxxxxxxxx
> Subject: Re: [ARSCLIST] Video degeneration
> Can someone please explain to me how video tape degradation
> differs from audio
> tape degradation? Seems like the only differences would be binders (more a
> product of the era in which it was created than anything else) and casing.
> Otherwise, there should be very little difference at all.
> In other words, isn't magnetic tape just....magnetic tape?
> Period. Regardless of
> the playback medium or material that one can capture over the
> other? Again,
> this is with respect to whether or not they have a cellulose
> acetate backing,
> Brandon Burke
> Brandon Burke
> Graduate Research Assistant
> Digital Library Services
> University of Texas at Austin
> Austin, TX
> phone: (512) 495-4439
> email: bburke@xxxxxxxxxxxxxxx