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Re: CDs, was DATs, Was Re: arsclist Duplicating casette tapes

At 01:21 PM 8/9/2002 -0700, Steve Green wrote:
I'm not jumping into the fray here and not lobbying for or against anything
in particular but--

On April 16, 2001 I took a Quantegy gold CD-R with audio tracks recorded on
it and placed it leaning up on a window sill here in northern Nevada. The
CD-R was thus exposed to full sunlight everyday, plus the full strength of
the sun's heat in summer and cold winter temperatures (not sub-zero because
it was on the inside of the window...). I did this as a simple real world
experiment, more for curiosity than anything else, to see how well CD-R
would hold up under intense UV radiation and fluctuating temperature
"extremes." A few months later, I popped the CD in a player and it worked
fine. I returned the disc to it's resting place on the window sill and left
it there undisturbed until today. Inspired by the current ARSC list
discussion, I just now took the same CD-R, blew the dust off it with
compressed air, stuck it in a Mac G4 CD drive and voila, it played fine--
at least, it recognized all the tracks fine. I haven't played it through
from end to end, just a few seconds of each track. Also, at the moment we're
not set up here to measure BLER so I can't say what's really going on with
the CD-R but we are now talking about a disc exposed to "elements" (some
anyway) for a year and four months (a winter and almost two summers) and the
information is still retrievable. Though not a scientific experiment, it has
certainly eased my mind considerably about the robustness of CD-R as a
storage medium/format.

Anecdotal reports are not to be dismissed, but neither are they the basis for choosing an archival medium. For example, it is difficult to infer anything about UV exposure on this test since the sunlight passes through glass - essentially opaque to UV - before striking the disc. UV exposure has little relationship to the environment of an archive (storage or in use). Even the effect of heat is debatable: it will certainly accelerate decay, but I have found no data which would lead to quantifying acceleration of life test as a function of storage temperature.

A well-written CD-R stored under favorable conditions and handled with care can be expected to last a long time. (Unfortunately, caddy drives are out of style; with them, the disc can be stored and used without being handled at all.) One approach is to record onto two different media and periodically to check each copy for errors. If one begins to develop errors, a fresh copy can be made from the other archive and the flaky one (a technical term beyond the scope of this essay) retired.

Note that as Jerry has pointed out, BLER is not a sufficient measure of quality. However, it may be adequate for purposes such as identifying the faulty disc in an archived pair.



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