The Basics of CD quality and compatibility

Feb 22, 2002

The Bottom Line Purchase a good brand of cd and try them. There is little indications of cd quality on a box.

It is interesting working in an electronics section of a retail store. Half of the people I meet, my customers, assume they know more about the products than I do. Often it is very true about many products, but one area that I have found most don't is cd-r and cd-rw media. Having done my simple research on the subject, I find that better than 95% of the people I talk to don't know much more than "if it's cheap then it might be bad".

After this half the people that know what they are looking at are smart. They ask. Unfortunately most of my coworkers don't know anything more about them then the customers. Which makes for a very confusing situation.

The other half isnít as smart as they assume with no evidence that any word in the title or on the package implies a quality factor. This is often, but not always wrong. I pity these folk for how much they unknowingly gave the music industry in fees. It is for both of these groups I am writing this, again. Except this time it will have much more information for you to explore.

The first idea to know is a written (or pressed) cd-r media is more likely to work in your cd-rom then your cd player usually. This is because cd players usually have one form of error correction: skip a fraction of a second. Where cd-roms have to have accurately read the data for programs and always have several levels of error correction.

In the above paragraph you may have noticed that I said written (or pressed). A laser writes to cd-r media you buy in a store. Your favorite music cd however is pressed in a mold and unlike cd-r media is one layer of metal instead of die.

Music vs Data:

Now what will you find when you go into a store? You will run into the same issue of there being two different kinds of cd-r media. They are music, aka digital audio, and data cd-r media. Most people will probably tell you music cds are better for music. That's not quite true. The difference between the two is actually quite small. You see music cds are made of the same dies with the same die process as data cds. The difference is that music cds have a small code written to them stating they are music cds. This is required in many consumer standalone music copiers including audio cd copiers and burners built into stereo system. CD writers in computers with exception to old cd writers ignore this code and write. The exception with some old cd writers is they might interpret the cd as already written to. Audio cds are more expensive because a fee is paid to the music industry for every cd. So, in general there is no difference between an audio and data cd as far as a computer is concerned. Unless you have a writer in your stereo you are just spending more money when buying a music cd-r media.

CD die color:

There are a number of other myths to see as well. My favorite is that blue cds are low quality, gold is good quality, and silver is excellent quality. Many people use this as referring to what is said on the box. The if the title has silver it is great quality. That generally is not a good idea. Generally there is nothing to show this. The cds they will buy will be made of every type and fabrication process for every one of these.

Another way this is interpreted is to look at the color on the underside of the cd and claiming that silver color is best. The idea being that certain colors reflect light better than others. The first problem here is that the laser reads a wavelength in a spectrum that isn't visible to the human eye. Thus the colors of a dark die on a cd are just as bad as a light die to the reading laser of a cd-rom or cd player.

Pigments of cds and their affects:

Color of the underside may be indicative of its lifetime.
When the underside of a cd is gold it is usually made of a die called: PhthaloCyanine. When you see a blue or silver it is usually: Cyanine. PhthaloCynanine made cd's last for about 100 years or sometimes more. Cynine cds don't reflect light as well, because of which they may last only 10 years with older made cds or 30 to 50 years with newer versions of this pigment. It is here that light reflection is an issue.

While PhthaloCyanine may last forever it has another problem. CD media made with it has a different requirement for writing lasers and to a small degree isn't compatible to
as many writers as CD media made with Cyanine. An interesting tradeoff it is: Lifetime vs compatibility. It isn't anything to worry about. The difference in compatibility is small.

Recording speed:

Another detail I hear is if you burn at a slower speed you will get better made cds. This is and isn't true. I'm afraid another tradeoff is present. CD media needs a certain amount of power in the burning laser to write. The faster you go the less time the laser has in each spot and the less a cd-r may pick up. This is why media is rated for certain speeds. The trick to get media to write at faster speeds is to use more sensitive dies in the media.

This means the slower you go the less error your cd makes right? NO. The burning cd laser is designed to run at a higher speed and is compatible, but makes more mistakes at slower speeds. Another problem with burning at slower speed is that is a sensitive disk will pick up too much if a laser is at one spot too long. So, it varies. Just don't run a 24x burner and 24x media at 2x. It would probably work, but dramatically increases the number of errors possible.

Compatibility vs. Quality

Say your friend burned a hundred cd-rs of a brand and they run just fine in all of your stuff. Will that mean the cd-r media is a good quality and will work in your cd writer? Not unless you have an identical model of cd burner. Different cd writers have different laser techniques. Just because cd-r media does or does not write correctly in one cd writer does not mean it will work the same in another. Like people, every cd writer is different yet fundamentally the same, try a few brands of cd media if one doesn't work in your cd-writer.

80 minute, 700 megabyte vs 74 minute, 650 mega byte cd media

Bigger is better, right? Not necessarily, they almost always work, but in order to make them larger makers had to minimize or reduce tolerances for margins of error. Meaning a 80 minute disk is more likely to have problems after being written to then a 74 minute disk. Just as the new 99 minute disks are frequently more incompatible than the 80 minute disks. Usually it's not an issue, being media is cheap. If one cd is bad just burn another.

I believe I've touched everything I can think of. Here are a few links in case you would like to do more research. - different forms of answers to questions. - Usenet FAQ - most question are answered here.

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