Plenty of people have written stuff about CD's. How to burn them and what CD's are better than others. They go on about audio CD's, data CD's, video CD's and most of what they talk about is absolute waffle. It's straight off the manufacturers brochure and only highlights how little they know about the things.

All CD's store data. Just data and nothing else. There is no magical little green man inside the CD saying "Oh look, this is audio data and that is video data and look over there is a bit of text data". The big confusion with people thinking there is some difference comes about because of the way a disc is formatted but not because of the way the disc is physically made. So let us make this one thing clear, all CD's are manufactured to store raw data.

We all know that a CD is constructed using a clear poly carbonate (plastic) disc adhered to which is, a dye, a reflective layer and then generally a lacquer to provide a protective cover. There are various bonding techniques and some manufacturers may use additional protective layers but we are not here to discuss those. The CD burner makes unperceivably small holes in the dye allowing the reflective layer to shine through. Simple stuff and as we said before, you can generally read that type of information off brochures. Once upon a time, the whole process used to be considered very technical but now (just like IC's and other clever modern components), they are stamped out in the billions and no body thinks anything of it.

Now don't get excited and think we know a great deal more than the so called "experts", because we don't. Fact is, as regards their life expectancy, CD's are almost impossible for us mere mortals to test. It requires equipment more sophisticated than most of us posses. By the way, have you ever read the fine print on a CD manufacturers life guarantee. It generally goes along the lines of "Lifetime warrantee but only when held east, facing a strong wind and protected by rare speckled camel dung", etc, etc. Conditions that are impossible in normal life. But lets get back on track and face facts, the guy in the street cannot even check the readable surface condition of a CD. And as regards it's life expectancy, that is left to the willingness of manufacturers to put their nuts on the line and say "Our CD will last this many years XXXX". Sadly, none of us are going to live the 200 years to prove them wrong. But, as always, we have taken a lot of this stuff apart and come up with what we think are some very practical suggestions.

The highly technical Gear Plus CD longevity test.

Thankfully we have devised a few simple tests to help most poor punters put their minds at rest. First you have to be prepared to waste a couple of CD's. It's a small price to pay for peace of mind. Now our crude yet very effective testing system consists of the following.

1. Having read all the promotional blurb and narrowed your choice down to the few brands you think will be OK, take a couple of CD's from the box of each manufacturer to use as test CD's. You can even label them test1, test2, test3, etc (using a soft felt tip pen).
2. Find a surface that you are certain is flat (like the top of your head). Lay your CD on this flat surface and turn it to see if it has any buckles or bumps. If it has any buckles, just ditch the thing straight away. At this point, you may want to check if the remainder of the batch is the same because over time, these CD's will inevitably fail in a number of machines.
3. Now, spin each test CD and check if the tracks run evenly. It's not hard to do. Hold it with a pen through the centre hole. Give it a spin and look along the disc sideways. You can see the tracks in the reflected light. Once again if they don't pass this test, chuck the things out. They are not worth persistence.
4. A small amount of patience is required for the next challenge. Leave your test CD's laying in the sun for a few days. Then as a reference, check them each day against new CD's straight out of the packet. Hopefully you will be able to notice which has discoloured the most. Obviously you will scrap the brand that discolours first.
5. Now for the real test and this ones an absolute eye opener. Put a drop of water on each test CD and then just wait a while. It's interesting, on the lesser quality CD's, you will generally be able to watch the the organic dye force the reflective coating right off the plastic disc. You will be surprised at just how poor the protective surface is on some of these CD's. Surely, we don't have to say anymore. If they fail this test, place them immediately on the scrap heap with a no return sticker.

Treatment of CD's.

Now from this testing you may or may not have made up your mind about which CD's you are going to run with. One thing you will have noticed is that CD's seem to have a lot of the same problems that magnetic tape always suffered from. So, what ever CD's you decide to go with we suggest you adhere to the following when storing them.

• Store them in a dust free environment. CD's being plastic love to attract dust and as such are then prone to scratching. Don't get sucked into spraying them with any anti static solutions. That will only do more harm than good.
• Obviously, sunlight is a big killer of CD's but then so is excessive room lighting. It's preferable to store your CD's in a box or some other covered device that excludes light of any sort.
• Temperature is also the scourge of CD's. But there are really two issues here. One being that the dye is temperature sensitive so you want to avoid extremes of temperature, particularly avoid hot places. The other issue is variance of temperature. It is important to avoid frequent changes in temperature as it tends to play havoc with the various layers and the bonding of each. Once again, it's the same problem as found in magnetic tape, only worse. Different materials expand and contract at different rates, so when a CD changes temperature, each of it's components expands at a different rate. The reflective layer reshapes itself slightly each time and the bonding layers get a hiding. In the long run they do not so much break down as just change structure into something a CD player cannot read.
• One of the big killers of CD's is humidity. Don't think that just because your CD is made of plastic that it is impervious to moisture. Some of the parts that make up most CD's are water soluble and as such take on moisture nicely. So, be very very careful of placing your prized CD's in nice dark corners. They may be out of the sun but they may also be in an area that is high in humidity and one little bubble or flake caused by moisture is going to ruin the whole project.
• Another point often overlooked is how people stack CD's. Do not stack them flat and certainly do not stack them on top of one another. Stack them vertically on edge and with nothing else pressing against them. Avoid commercially made racks that lay them flat. These racks are normally made by cabinet makers who know absolutely nothing about the manufacture of CD's. The last thing you want is to pull a CD from it's rack, after storing it for a few years, to then find it looks more like a banana.

CD burners

Now just as a last word about speed of burning. CD burner's generally have a sweet spot just as most every other piece of electrical equipment does. We all know that amplifiers, speakers, microphones, etc, etc have their highest distortion at each end of their specified range and so do CD burners. It may take some time for you to find the sweet spot for the media you choose but you can bet your boots it will be very unlikely to be the fastest or the slowest setting. As always, with anything audio, trust your ears.