Subject: [7-4] Which kind of media should I use?
(2000/11/03)
There is no "best" media for all recorders. You can't tell how well a disc
will work just by looking at it; the only way to know is to put it in
*your* recorder, write a disc, then put it in *your* reader and try it.
Statements to the effect that "dark green" is better than "light green" are
absurd. Some discs are more translucent than others, but that doesn't
matter: they only have to reflect light in the 780nm wavelength, not the
entire visible spectrum. See (7-19).
It may be a good idea to start by selecting media that is certified for
your recorder's desired write speed. This is particularly important for
CD-RW discs, which won't be written faster than the disc is rated for,
regardless of the top speed of the drive. Using 8x-certified CD-R media
when recording at 8x isn't a bad idea, but doesn't seem to be essential.
See section (3-31) for some other remarks about recording speed.
The Orange Book standard was written based on the original "green" cyanine
discs from Taiyo Yuden. Cyanine dye is more forgiving of marginal read/write
power variations than "gold" phthalocyanine dye, making them easier to read
on some drives. On the other hand, phthalocyanine is less sensitive
to sunlight and UV radiation, suggesting that they would last longer under
adverse conditions.
Manufacturers of phthalocyanine-based media claim it has a longer lifespan
and will work better in higher speed recording than cyanine discs. Mitsui's
gold/gold discs are recommended by some vendors, and in some informal and
unscientific tests were more compatible with car CD players than Kodak
gold or TDK green discs. The response to Mitsui's "platinum" media has
also been favorable. Different test labs will tell you different things.
See http://www.cd-info.com/CDIC/History/Commentary/Parker/stcroix.html for
some notes on low-level differences between media types.
There is no advantage to using expensive "audio CD-Rs". There is no
difference in quality between consumer audio blanks and standard blanks
from a given manufacturer. If you have a consumer audio CD recorder, you
simply have no other choice. There is no way to "convert" a standard
blank into a consumer audio blank. See section (5-12) for notes on how
you can trick certain recorders into accepting standard blanks.
Trying samples of blanks is strongly recommended before you make a major
purchase. Remember to try them in your reader as well as your writer; they
may not be so useful if you can't read them in your normal CD-ROM drive.
Maxell's CD-R media earned a miserable reputation on Usenet. In April
'97 Maxell announced reformulated media that seemed to work better than
the previous ones. It appears they may no longer make their own media.
Some good technical information is available from http://www.mscience.com/.
In particular, "Are green CD-R discs better than gold or blue ones?" at
http://www.mscience.com/faq52.html.
BLER measurements for a variety of recorders and media is in a big table
on http://www.digido.com/meadows.html.
See also "Is There a CD-R Media Problem?" by Katherine Cochrane, originally
published in the Feb '96 issue of CD-ROM Professional.
Subject: [7-5] How long do CD-Rs and CD-RWs last?
(2000/10/17)
There doesn't seem to be a clear answer for CD-RW. The rest of this
section applies to CD-R.
The manufacturers claim 75 years (cyanine dye, used in "green" discs), 100
years (phthalocyanine dye, used in "gold" discs), or even 200 years
("advanced" phthalocyanine dye, used in "platinum" discs) once the disc has
been written. The shelf life of an unrecorded disc has been estimated at
between 5 and 10 years. There is no standard agreed-upon way to test discs
for lifetime viability. Accelerated aging tests have been done, but they
may not provide a meaningful analogue to real-world aging.
Exposing the disc to excessive heat, humidity, or to direct sunlight will
greatly reduce the lifetime. In general, CD-Rs are far less tolerant of
environmental conditions than pressed CDs, and should be treated with
greater care. The easiest way to make a CD-R unusable is to scratch the
top surface. Find a CD-R you don't want anymore, and try to scratch the
top (label side) with your fingernail, a ballpoint pen, a paper clip, and
anything else you have handy. The results may surprise you.
Keep them in a cool, dark, dry place, and they will probably live longer
than you do (emphasis on "probably"). Some newsgroup reports have
complained of discs becoming unreadable in as little as three years, but
without knowing how the discs were handled and stored such anecdotes are
useless. Try to keep a little perspective on the situation: a disc that
degrades very little over 100 years is useless if it can't be read in your
CD-ROM drive today.
One user reported that very inexpensive CD-Rs deteriorated in a mere six
weeks, despite careful storage. Some discs are better than others.
By some estimates, pressed CD-ROMs may only last for 10 to 25 years,
because the aluminum reflective layer starts to corrode after a while.
One user was told by Blaupunkt that CD-R discs shouldn't be left in car CD
players, because if it gets too hot in the car the CD-R will emit a gas that
can blind the laser optics. However, CD-Rs are constructed much the same
way and with mostly the same materials as pressed CDs, and the temperatures
required to cause such an emission from the materials that are exposed would
melt much of the car's interior. The dye layer is sealed into the disc,
and should not present any danger to drive optics even if overheated.
Even so, leaving a CD-R in a hot car isn't good for the disc, and will
probably shorten its effective life.
See also http://www.cd-info.com/CDIC/Technology/CD-R/Media/Longevity.html,
especially http://www.cd-info.com/CDIC/Industry/news/media-chronology.html
about some inaccurate reporting in the news media.
See "Do gold CD-R discs have better longevity than green discs?" on
http://www.mscience.com/faq53.html.
http://www.cdpage.com/dstuff/BobDana296.html has a very readable
description of CD-R media error testing that leaves you with a numb sense
of amazement that CD-Rs work at all. It also explains the errors that come
out of MSCDEX and what the dreaded E32 error means to a CD stamper. Highly
recommended.
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