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Re: [ARSCLIST] Audio storage on external hard drives
on 2/23/05 6:31 PM, John Poirier at John_Poirier@xxxxxxxxx wrote:
> supporting the widely held perception that "gold dye" CDs are likely to
> survive aging much better than other types. Non-gold discs appear to be not
> only shorter-lived than gold dye but frequently outright lousy.
This is a widely-held misunderstanding of CD-Rs. I'm sure that Jerry will be
able to chime in here in with more details, but there is no such thing as
gold dye discs, what you are seeing is the gold reflective surface
underneath the dye. Gold is considered to be more archival because it does
not tarnish like silver or aluminum when exposed to oxygen. There are 2
basic dye types, Phthalocyanine and cyanine. Phthalocyanine is clear to the
eye, the disc appears to be the color of the reflective surface - therefore
the impression of the gold dye discs. Cyanine dye can vary from green to
blue in color, therefore the impression of green or blue dye discs.
Now for the nitty gritty. Generally speaking, cyanine dye works with a wider
range of laser power and tends to be more compatible, especially with legacy
burners. But it is sensitive to UV and can degrade if exposed to sunlight.
Phthalocyanine dye requires tighter control of laser power when burning and
can exhibit compatibility problems with certain burners. But it is not
sensitive to UV and is considered to be more archival. But there's more. The
CD burner is also a major part of the equation. Since dye formulations are
changing all the time, and as blanks become optimized for higher speed
burning, and as burners are capable of ever faster burning speeds, legacy
burners can slowly become incompatible with CDR blanks. Additionally,
burners do wear out - they have a limited lifespan and after a certain
number of discs the laser will no longer be able to calibrate itself to the
current generation of blanks therefore increasing the error rate.
So, just because a certain burner/CDR combination produced acceptable discs
in the past does not mean that it will continue to do so. As Jerry often
points out, regular testing is a necessary part of any archival CDR
operation. Mastering engineers, who are truly anal retentive about error
rate test every single disc they make. In fact, most mastering engineers use
cyanine discs because they tend to produce a lower error rate. Tayo Yuden
seems to be the preferred brand.
Director of Recording Arts
Associate Professor of Music
Indiana University School of Music