Compact Discs were developed in the 80, to supersede records. It's taken a while, but they've finnally become the standard for audio. Unlike records, they store data digitally, ie. as ones and zeros, just like computers. Consequently, the reproduction of the audio is far more accurate than with records. Also, because playera use a laser beam to read the discs (rather than a needle), CDs last a lot longe, since their not constantly being scratched. Even when slightly scratched they still work! Although this is the case, you should never touch the underside of a CD. Minidiscs use similar laser technology, to read their discs.

Recently, recordable CD-machines have come onto the market. CDs made in these machines can be played in any CD player (they cannot be erased though). However, rewritable CDs cannot be read by ordinary CD players and cannot be erased as many times as minidiscs! There is little point buying a standalone CD recorder, unless you don't own a computer. Computer CD recorders are cheaper, and have more features!

Like Minidiscs CD, store sound in 16 bit 44100 Hz format. However, they use no compression and store sound in PCM (Pulse Code Modulation) format. Computer wave format also uses PCM. Since no compression is used, no sound is discarded. New standards are arriving to take over from the CD, including Super CD (made by Sony and Philips) which uses a special DSM (direct sound modulation) recording system (instead of PCM). It supposedly delivers better dynamics. DVD Audio is another format which is recorded in 24 bit 96000 Hz format! Both DVD Audio and Super CD discs look the same as CDs, but require new machines (which can still play CDs). However, Super CDs have two layers, one which can be read by ordinary CD players and another which can be read by Super CD players. In addition these new formats have several channels of sound. CDs have two channels of sound (left and right).

In addition HDCDs are coming to the market. Most expensive CD players can read CDs encoded in HD. HDCDs also work in normal CD players.

Buying A Machine. CD Players come in all shapes and sizes, from portable machines to home-decks. Portable machines tend to be a bit bulky in comparison to their minidisc and tape counterparts. As in Minidisc players they have a laser which reads the disc. The digital data which it reads is then passed onto to a digital-to-analogue converter. This is outputed to the amplifier.

It is possible to buy a CD player in several units, where one unit is a CD transport which outputs a digital signal to another box which contains a DAC. This then outputs to a preamp, which outputs to an amplifier! Some hifi experts say that separating out the tasks this way, ensures that there is less interference between components. I am however, a bit sceptical.

Far more important, however, is the quality of the DAC. There are several different types of DACs. Some use bitstream, where they convert one bit (a one or a zero) at a time. Multibit DACs work on larger pieces of information. The DAC is not the part of the CD player which will influence the sound produced. Higher end DACs will have the capability of converting sound at 24 bit 96000 Hz. There are also delta/sigma DACs.

Home Decks. The price of CD decks can range from £100 to over £5000. The choice is far bigger than that available in the minidisc deck market. On certain machines, there are no remote controls or displays. The displays are said to interfere with the operation of a CD, and it is recommended that you turn the display off when playing a CD. Most decks have a "Display Off" button. This is trivial in comparison to most features. Much more important is the outputs available on the machine. If you are planning to buy a minidisc recorder, check that the CD player has an optical output connection. Many CD players may feature coaxial digital outputs, but few minidiscs recorders have these. In addition, certain CD players, have optical inputs, so that you can use their DACs. This is useful if you have other components like a minidisc player (with optical out or coaxial digital out) and would like to make use of a good quality DAC in your CD player. Jitter correction is also a feature which is employed by some CD players, that is misalignment between the laser pickup and the CD being played. If you rip MP3s, your software usually has a "Jitter Correction" feature.

Multiplayer CDs are generally of poorer quality than similarly priced single CD units, but have the advantage of being able to place several hours of music non-stop. In addition making complilation minidiscs is easy with multiplayer CDs. Some mulitplayers can hold hundreds of discs, like the Sony CDP-CX3.

If you want a future proof system, which is great at playing CDs, then a Sony Super CD system is for you. These are expensive though, as are other high end CD players. Also, we do not yet know which new format will be consigned to the dustbin, will it be Super CD or DVD Audio. It might be best to stick to buying a CD player at the moment. Because CDs and DVDs are the same size, DVD Video machines have been comptable with CDs. Most can play CDs, some as well as dedicated CD players.

If you buying a totally new hi-fi system, it might be tempting to buy an integrated system with a CD. This is easier to set up and smaller than a hi-fi seperate system. It does have the disadvantage of forcing you to buy all the components together. Mini systems are best for places where you must have a small unit and sound quality is not that important.