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CD-Recordable FAQ - Section 6
Subject: [6] Media This section covers recordable CD media.
The basic building blocks of CD-R media are organic dye and a reflective layer. The dye types currently in use are:
Discs come in many different colors. The color you see is determined by the color of the reflective layer (gold or silver) and the color of the dye (light blue, dark blue, green, or colorless). For example, combining a gold reflective layer with cyanine (blue) dye results in a disc that is gold on the label side and green on the writing side. Many people have jumped to the conclusion that "silver" discs are made of silver, and have attempted to speculate on the relative reflectivity and lifespan of the media based on that assumption. Until an industry representative issues a statement concerning the actual composition, it would be unwise to assume that the reflective layer has any specific formulation. Taiyo Yuden produced the original gold/green CDs, which were used during the development of CD-R standards. Mitsui Toatsu Chemicals invented the process for gold/gold CDs. Mitsubishi developed the metalized azo dye. Silver/blue CD-Rs, manufactured with a process patented by Verbatim, first became widely available in 1996. According to the Ricoh web site, the silver/silver "Platinum" discs, based on "advanced phthalocyanine dye", were introduced by them in 1997. They didn't really appear on the market until mid-1998 though. Kodak Japan holds the patent on formazan dye. See section (7-3) for vague details on who manufactures what. The reason why there are multiple formulations is that the materials and process for each are patented. If a new vendor wants to get into the CD-R market, they have to come up with a new combination of materials that conforms to the Orange Book specifications. Some CDs have an extra coating (e.g. Kodak's "Infoguard") that makes the CD more scratch-resistant, but doesn't affect the way information is stored. The top (label) side of the CD is the part to be most concerned about, since that's where the data lives, and it's easy to damage on a CD-R. Applying a full circular CD label will help prevent scratches. http://www.mitsuigold.com/ has some info on MTC media. You can visit http://www.ricohcorp.com/press/platinum2.htm for a press release concerning Ricoh's "platinum" media. An EMedia Professional article discussing the composition of the newer discs is online at http://www.emediapro.net/EM1998/starrett10.html. CD-RW discs have an entirely different composition. The data side (opposite the label side) is a dark silvery gray that is difficult to describe.
Yes. There are four factors to consider:
Some people have found brand X CD-R units work well with media type Y, while other people with the same unit have had different results. Recording a disc at 4x may make it unreadable on some drives, even though a disc recorded at 2x on the same drive works fine. To top it all off, someone observed that discs burned with one brand of CD-R weren't readable in cheap CD-ROM drives, even though the same kind of media burned in a different device worked fine. The performance of any piece of media is always a combination of the disc, the drive that recorded it, and the drive that reads it. A number of specific diveries have been posted to Usenet, but none of them are conclusive. Many people have reported that Kenwood CD players don't deal with CD-Rs very well, while Alpine units play nearly everything. However, things change as product lines evolve over time. Some users have found that the *quality* of audio recordings can vary depending on the media. Whatever the case, if you find that CD-Rs don't sound as good as the originals, it's worthwhile to try a different kind of media or a different player. See section (4-18) for other ideas. If you want to see what media test results look like, take a look at http://www.digit-life.com/articles/cdrdisktest/index2.html. One final comment: while there are clearly defined standards for CD-R media, there are no such standards for CD and CD-ROM drives -- other than that they be able to read CDs. It is possible for media to be within allowed tolerances, but be unreadable by a CD-ROM drive that can handle pressed discs without trouble. All you can do in this sort of situation is find a better-quality CD or CD-ROM drive, or switch to a brand of media whose characteristics are on the other side of the tolerance zone.
Taiyo Yuden made the first "green" CDs. They are now manufactured by TDK, Ricoh, Kodak, and probably several others as well. Mitsui Toatsu Chemicals (MTC) made the first "gold" CDs. They are now manufactured by Kodak and possibly others as well. Verbatim made the first "silver/blue" CDs. Most CD-R brands (e.g. Yamaha and Sony) are actually made by a handful of major disc manufacturers. Attempting to keep track of who makes what is a difficult proposition at best, since new manufacturing plants are being built, and resellers can switch vendors. See section (2-33) for notes about identifying the source of a CD-R.
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's probably a good idea to start by selecting media that is certified for your recorder's desired write speed. 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. Speed considerations are much more important for CD-RW. Many drives refuse to record at speeds higher than the disc is rated for. On top of that, there are "fast" blanks (for 4x-10x recording) and "slow" blanks (for 1x-4x). The "fast" blanks are labeled with a "High Speed CD-RW" logo. 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.
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 |