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

[mollyw@gslis.utexas.edu]

I am glad that I posted my earlier message. I had, in the case of
R-DAT vs. CD-R, sort of settled on thinking about it as I had learned in
the class I mentioned. It is valuable to receive other information,
especially as a student interested in this very matter.
Thanks!

Molly Wheeler

On Fri, 3 May 2002 jhartke@mscience.com wrote:

> mollyw@gslis.utexas.edu wrote:
> >
> > I recently took a course, Basics in Audio Preservation and
> Reformatting,
> > 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
> recorded
> > 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
> is
> > not linear, differs so much from the data on the neighboring track.
> > This can then cause migration, as the polarities will attempt to
> adjust,
> > 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
> are
> > 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
> it
> > is not the type of migration you mention, but it is an artifact
where
> an
> > 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
> coercivity
> > 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
> tape
> > - it will be very unusual for either to just change polarity. BUT
> having
> > said all that. There is no question that CD'r are the choice because
> the
> > 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
> paycheck
> > 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.
>
> Jerry
> Media Sciences, Inc.
>
>

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