Today there is a wide range of CD players available for the consumer and choosing the right CD player can feel like an arduous task. Style, quality, design och technical solutions vary greatly between the different players. Some players are portable; others are included in larger sound systems. Some players can only handle one disc at the time; others can easily skip between 50 discs or more. Some CD players are very cheap, others are highly expensive. The list goes on and on. Regardless of which CD player you choose it will however consist of three basic parts that are found in all moderns CD players: a drive motor, a tracking device and a laser and lens system. Another thing that all CD players have in common is that they interpret data that has been stored in the form of elongated bumps on a CD (compact disc).
The drive motor in your CD player is the part that makes the disc spin round and round at a correct pace. The drive motor will gradually adjust the speed, since the correct pace depends on which part of the disc that is currently being interpreted. At some spots, the pace will be no higher than 200 rpm, while at other spots the pace needs to be increased up to 500 rpm. As the disc is rotated round and round by the drive motor, the tracking mechanism will adjust the laser assembly and make it possible for the laser and lens system to focus on the minuscule bumps where data has been stored. The laser is constantly being pushed from the centre and outward over the disc by the tracking mechanism.
The data interpreted by the laser and lens system has been stored in the form of elongated bumps on the surface of the CD. One single bump is very small and no wider than 0.5 microns. The height is greater than 125 nanometres and the length is 0.83 microns or slightly more. All these bumps are very neatly organised at the surface of the CD in the form of a 5 kilometre (3.5 miles) long spiral.
The CD itself is made up by several different layers, including a polycarbonate layer and an aluminium layer. When the laser tries to interpret data that has been stored on the CD, it will first penetrate the polycarbonate layer. The aluminium layer will then reflect the laser beam, and the light alterations will be detected by a special optoelectronic mechanism in the CD player. Since the bumps in which data has been stored reflects light in a different way compared to the areas between the bumps (commonly referred to as “lands”), the CD player can determine exactly which parts of the disc that is made up by bumps and which parts that are not.
If a CD is scratched or injured in any other way, it can be impossible for the CD player to interpret it. Sometimes only a minor part of the data will be skipped, but larger damages can render the entire CD useless. Always store your CD’s in a protective casing to decrease the risk of scratches. When you clean your CD’s, carefully move your hand from the centre and outwards to the edge rather than just swabbing around. Scratches that occur from a radial movement tend to be less damaging than other scratches.