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The Truth About Media Color
by Bob Starrett
http://www.cdpage.com
Everyone has their favorite brand or color of media (blank recordable
CDs). When we make a good disc we like the media. When we make a bad
disc we don't like the media. If most good discs are blue, then we
like
blue. If we make some bad discs with Brand X media, then we don't like
Brand X media. But, despite all the postings and controversy over which
color or type of media is best for which recorders, the truth is that
it
really does not matter in most cases what kind of media you use, if
everything else is working properly.
This is not to say that some media doesn't indeed work better in some
recorders. But the main question may be: What do we mean by "works"?
Do
we mean 100 percent success? Do we mean that recording is successful
most of the time? Do we mean that some media has significantly lower
error rates than others when used in a certain recorder?
Drive manufacturers are well aware that some media work better in their
recorders than others. When TEAC first released its R55S 4x recorder,
its firmware would only allow writing to certain media. The recorder
actually looked at the media, and if it was not an approved brand,
the
recorder would return an error message. Unfortunately, not all recording
software explained the error clearly, so many people were convinced
that
certain media did not work in that TEAC recorder. And they were right:
certain media did not work. But was that a problem with that media?
No,
it was a decision by TEAC that the excluded media would not work as
well
as they wanted it to, hence to try to avoid problems by excluding it.
Would that same media work in other recorders? Of course it would.
It is interesting to note that, on the whole, recorded media, no matter
what color or dye formulation, have significantly lower error rates
than
pressed (factory-made) CDs. So, no matter what media you use, it is
likely that your finished discs are of better quality than that Windows
2000 pressed disc that you just bought.
All the Colors of the Rainbow
-----------------------------
The different colors you see in CD-R media are a result of the
combination of the dye formulation used, the composition of the
reflective layer (gold or silver), and sometimes the top coating used
on
a disc.
CD-R makers uses three kinds of organic dye for the recording layer
of
CD-R media: Cyanine, Phthalocyanine, and Metal Azo.
The cyanine dye is blue, but cyanine-based media usually appears bright
emerald green, because it's matched with a gold reflective layer.
Phthalocyanine dye is pale green, appearing yellow-green on a
gold-backed disc.
Metal Azo dye is deep blue, and looks that way when matched with a
silver reflective layer, or it appears green when used with a gold
reflective layer.
The aqua-hued Advanced Pthalocyanine is also now in wide use.
So What's in a Color?
---------------------
Phthalocyanine dye is less sensitive to ordinary light -- incoherent,
random light such as sunshine, ultraviolet, incandescent, and
fluorescent light normally found in the real world outside of CD
recorders. That means that prolonged exposure to bright light --
particularly bright UV light -- will render cyanine media unreadable
sooner than phthalocyanine.
Phthalocyanine will probably last longer and preserve information better
under these adverse, but extremely unlikely conditions. If we store
information on CD-R media that is so valuable as to merit preservation
for a long period of time -- say 30 years or more, assuming, of course,
that there will be hardware capable of playing the disc at that point
in
the future -- are we going to leave those precious discs lying out
in
the light and heat? No, we are going to store them carefully in their
jewel cases, away from the light, heat, and scratches that are the
biggest threats to data loss. Then again, if an application does not
require that the data remain readable 30 days from now, who cares if
the
data fades in 50 years or 100? The important thing is how reliably
the
disc can be written and read _today_.
That is the other side of light sensitivity, and it's a significant
one.
Phthalocyanine dye has a narrower range for writability with laser
light
- the coherent, tightly focused and precisely calibrated light used
in
CD recorders. The recommended range of laser power for phthalocyanine
dye is 5mW, plus or minus .5 mW. The range for cyanine dye is 6mW,
plus
or minus 1mW. This wider power margin may mean that cyanine media is
suitable for a greater range of recording speeds and laser powers.
It
may also mean that cyanine media offers a higher likelihood of
compatibility with more CD recorders.
Compact discs use pits of varying lengths to represent data. The pits
are the same width and depth, but their length and the spaces between
them vary. The shortest pit is a 3T pit, and the longest, 11T. In CD
recordable, the pits are replaced by optical marks that, when read
by a
CD player or CD-ROM drive, appear similar to the pits in molded CDs.
The
lengths of the pits or marks are time-relative, not absolute; that
is,
the length is a function of disc spin. A disc that spins at a rate
of
1.2 m/s while being recorded will contain marginally shorter 3T to
11T
pits than a disc that spins at 1.4 m/s. It will also contain more of
them, which allows for greater disc capacity, but that's a topic for
another time.
Using laser light to create a microscopic mark of a certain length on
dye polymer is not a linear process. Because materials tend to respond
differently when they are heated for different lengths of times, a
laser
setting that produces a light pulse that creates a mark of a given
length does not necessarily produce a mark twice as long when the light
pulse is twice as long. Similarly, a laser setting that produces a
light
pulse that creates a mark of a given length in one type or brand of
media does not necessarily create a mark of that same length in another
type or brand. This problem is compounded by the reading drive's pickup;
optical effects can alter the perceived length of a mark, so that what
has been recorded may not be the same as what is read.
The results of this discrepancy between what is read and what was
intended to be written can vary from unreadable discs, to discs with
a
high rate of errors due to jitter. To compensate for this, recorders
can
selectively boost or shrink the lengths of individual marks by using
a
write strategy. This effectively modifies the pit length signature
of a
recording medium so that the detected signals correspond to the input
data patterns.
CD recordable technology is complex and convoluted. There are many
factors that come into play when recording a disc: the rate of spin,
the
formula of the dye, the ambient temperature, the internal temperature,
the age of the media, the power and wavelength of the laser, and the
spacing and size of the marks on the media relative to the speed of
the
disc -- to name but a very few. Media manufacturers constantly adjust
the myriad factors of disc production, including but certainly not
limited to the formula of the dye. CD-R media must combine the
properties of compatibility, writability, readability, and data
longevity. To say that a certain dye formula or brand of media is
inherently better than another based exclusively on one of these
properties is not only simplistic, it is misleading.
There are not sufficient data to show that any one media dye formulation
or reflective layer is better than another. The best rule of thumb
is to
find media that works well for you, and and stick with it.
***************************************
Another article on this topic:
http://www.adaptec.com/tools/compatibility/bestmedia.html
If a technical term is unfamiliar to you, you can look it up in the
CD-R
Glossary:
firmware <
http://www.adaptec.com/tools/glossary/cdrec.html>
***************************************
All contents copyright Adaptec, 2000. Contents may not be reproduced
in
any form without written permission from Adaptec.
***************************************
--
Best regards, Deirdre' Straughan
"Largo al factotum del CD-R"
CD-R Software: http://cdr.adaptec.com
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http://www.adaptec.com/adaptec/registration/cdrnews.html
CD-R Discussion List:
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Some resources on the Adaptec Web site:
Adaptec CD-R Software - http://cdr.adaptec.com
Great deals on CD-R media -
http://www.adaptec.com/mediaboard/index.html
The CD-R Database -
http://www.adaptec.com/cgi-bin/cdrmain.cgi
Adaptec Support Knowledgebase:
http://ask.adaptec.com/cgi-bin/tic
Adaptec CD-R Info Grid -
http://www.adaptec.com/products/overview/cdrgrid.html