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Re: [AV Media Matters] CD-R vs. R-DAT

mollyw@gslis.utexas.edu wrote:
> I recently took a course, Basics in Audio Preservation and
> here at the University of Texas at Austin, as part of my archives
> cirriculum. In this class we covered this very issue, CD-R vs. R-DAT.
> While many people are using R-DATs for their preservation copies of
> sound
> recordings, they pose a serious problem.
> Since R-DATs are a helical scan tape technology, the tracks are
> as diagonal stripes along the tape. The fundamental perservation issue
> in
> this is that  stored data at any given point along a track, since it
> not linear, differs so much from the data on the neighboring track.
> This can then cause migration, as the polarities will attempt to
> and information lost will have a much bigger effect on the integrity
> of the DAT tape than it would a tape with linear tracks. So, it seems
> as though CD-Rs are a wiser choice for preservation purposes.
> I hope this helps.
> Molly Wheeler
> Student, University of Texas at Austin
> Moderators Comment:
> Well you need to talk to your professor - and tell him/her that almost
> all recordings these days are helical, and that almost all recordings
> these days don't have guard bands between tracks (space between them)
> and therefore have one magnetic area right next to another and
> furthermore use azimuth recording techniques which mean that tracks
> laid up right against one another. But almost NO recordings have bits
> that spontaneously move around and change polarity. T there are many
> techniques used to spread the data and make it redundant so that data
> loss is recoverable, but usually the loss is not the type you mention
> anyhow. Magnetic fields generally don't "migrate" unless there is a
> reason to. You might consider print through a migration of sorts, but
> is not the type of migration you mention, but it is an artifact where
> area of high energy is in DIRECT proximity/contact with an area of low
> energy. The migration (or lack thereof) will also depend on the
> coercivity of the tape being used. Most modern media is high
> which means that a relatively strong field is needed to reverse an
> existing field of magnetic energy on a tape. So if a positively biased
> particle is next to a negatively biased one - on a high coercivity
> - it will be very unusual for either to just change polarity. BUT
> said all that. There is no question that CD'r are the choice because
> alternative is almost an obsolete format - clearly endangered.
> Right answer - wrong reason. But don't tangle with the prof. yourself
> send him/her to me!! We don't want you're "A" for the course to
> spontaneously turn into a "B"  - or for that matter the prof's
> to go from $5,000 to $500 after it was stored for a while would we??
> Jim lindner

We tested 4 mm and 8 mm helical scan tapes for several years, and agree
with Jim. One problem with tape is that read/write heads are in-contact.
High head velocities can result in head clogs that adversely affect the
drive or can damage small regions of the tape. Longevity tests use
repeated write/read passes over the same area, and subsequent read-only
tests clearly show errors from debris that has piled up at both ends of
the longevity test area.  Helican scan tapes use complex Reed-Solomon
Product Code error detection and correction that can handle most damage
but archival risks are present.

Media Sciences, Inc.

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