TIP # 4:
The compact disc has revolutionized the way we listen to music. Its advanced technology has put the caliber of sound, found previously only in the most exotic high end systems, within reach of just about everyone. But, though it has found its way into most peoples’ music systems it remains a thing of mystery. Here are some interesting facts and tips. The disc itself is a wafer thin piece of aluminum, laminated in plastic. The metal disc has billions of holes in it, radially. The recorded information begins at the centre of the disc and progresses outward (unlike an album which is read from the outside-in.) The plastic laminations protect the metal from damage. The playback system of a CD player utilizes a laser beam which is focused on the series of holes. A photo sensitive eye is positioned to receive the beam as it reflects off the shiny metal. When the beam is interrupted by a “pit”, a computer notes the change. When there is no change in the reflection -this is also noted, resulting in a stream of two pieces of information ( e.g. 1001101010001) called a binary code … digital. This information is sent digitally, via an error correction computer, to a converter which then changes the binary code back to music. Since the informational strip for one rotation is considerably longer on the outer edge of the disc than the centre, the disc must change speed constantly as it plays, starting at around 7OO rpm and ending at around 200 rpm. The CD is not indestructible, nor is it impervious to scratches dust and fingerprints. Since it is read with light, blemishes in the plastic will refract light and the information to the photo cell will be impaired. Some CD players have very good error correction Computers (the better the player the better the error correction) which can interpolate the tens of thousands of bits of wrong information. However, keeping in mind that ten or even fifty thousand bits of information will occupy a very small area of the disc, and since the CD player interpolates, or gives its best guess at what should be there, it can be wrong. The disc will sound its best with no imperfections on its surface, so, its a good idea to handle them with care as you would an album, and try not to slide them on surfaces that can scratch. The metal disc is laminated four times on the playing side (since there are holes in the disc , it will only play on one side) and only once on the label or upper side. The information is closer to the upper side making it is easier to damage the disc by scratching on the labelled non playing surface. If the disc gets smudged it can be cleaned with a non abrasive plastic cleaner. There are many good products available, from specialty CD cleaners to plastic lens cleaners It is important to use a soft clean cloth and to wipe from the inside of the disc toward the outside, not in a circular motion. This will ensure minimum scratching and, if a scratch should occur, it will not be over a long section of data. Scratches on a disc can be polished out with CD polish. This product has been developed specifically for the plastic from which CD’s are made, will remove the worst scratches and restore the optical linearity thus preventing the plastic from becoming a lens. Polishing removes some of the protective plastic surface, so don’t over do it. Beware, household polish can damage CDs! When CDs were first introduced, manufacturers included with them instructions on how to remove the CD front its case, recommending that you place your thumb on the retaining bump in the centre of the case with your index finger over the edge of the disc, before gently pulling up while pushing down on the bump. The disc then comes out of it’s case with less flexing and is more easily placed in the CD player. Since the disc is read by laser beam, with no physical contact to its playing surf ace, it can only be degraded only when it is not being played, ironic isn’t it? With a little care on our part the disc will last virtually forever, but what about the player itself? Although the compact disc player should require very little service throughout its lifetime, we should keep in mind that dust makes things blurry, and since most lasers point up inside the unit it is possible to get a buildup of dust on the laser lens itself. When this happens the CD player must work harder at interpolating and may skip some information. The drawer on the CD player should be kept closed whenever possible to minimize the risk of dust entering the unit. One last note, if, years after your CD player purchase you suspect a dirty laser, try a CD laser lens cleaner or take it to a service depot. Don’t take the top off the unit, unless you are a technician. The manufacturer of the player doesn’t put the warning sticker next to the laser assembly for nothing. It reads, WARNING : DO NOT STARE INTO LASER WITH REMAINING EYE
