Facts about CDs

The compact disc is a miracle of modern technology. Here are some facts:
  • They are made principally of injection-moulded polycarbonate.
  • The diameter is 120mm.
  • They are 1.2mm thick.
  • They contain up to 680 megabytes of data. This is the equivalent of 250,000 double-sided leaves (500,000 pages) of A4 text (which would be 83 feet high and need 8 trees to make).
  • The music on a CD is imprinted in the form of pits of varying length on a spiral track 3.52 miles (5.66 kilometres) long.
  • There are approximately 16,000,000,000 pits 0.11 micro-metres deep.
  • The largest pit dimension is 3.054 microns; the smallest is 0.833 microns.
  • The width of the pits is half a micron -- which is the distance a human hair grows in two minutes and a fingernail in seven minutes. It is 700 times smaller than a pinprick.
  • The space between tracks is 1.6 micro-metres.
Read by a red-light laser beam, the CD plays from the centre to the edge, rotating at a speed varying from 400 times a minute at the beginning to 250 times a minute at the end. This is equivalent to flying round the earth one inch above the surface, up to 400 times a minute, counting every blade of grass on the way.

Your CD is read by the laser beam and makes over 44,000 arithmetical calculations every second in at least two dimensions. It is adding up columns of numbers ('digits'). But many of the numbers are missing because there are thousands of errors on the average CD. Therefore the numbers are added up laterally as well as vertically, enabling the CD-player to fill in the missing numbers by cross-checking them. This is all quite normal and is called 'error correction'.


In proportion to the enormous quantities of CDs which are manufactured, faulty ones are extremely rare -- far far fewer than was the case with long-playing vinyl discs.

We at Hyperion receive about 100 to 150 so-called `faulties' per year, returned from customers. In addition we receive a similar number of reports of faulties (by phone, letter, email etc). That makes a total of about 300 complaints a year. Of those, perhaps 3 only are found to be justified and the discs in question truly faulty.

The 'fault' most commonly reported is failure to play -- usually one or two tracks, but sometimes the entire disc. This is one of the greatest mysteries of CDs: Why does a certain disc fail to play on a particular machine? Frequently a customer complains that a particular CD 'won't play' or 'jumps'. They usually say that they've never encountered the problem before and every other CD plays perfectly well on the same machine, therefore there must be something wrong with the disc. Upon being advised to try the CD on another machine they are usually nonplussed to find that it does in fact play perfectly satisfactorily, with nothing apparently wrong with it. This puzzling fact can lead to all sorts of strange cases. One disc was replaced for a Hyperion customer no fewer than NINE TIMES. In every case the replacement disc was tried, and found to be satisfactory, before being sent. They all refused to play except the ninth copy! And yet they were all identical and from the same pressing run. And not a single complaint was received from any of the other 15,000 people who had bought the same CD. One Hyperion artist was sent six copies of one of his CDs soon after issue. "They're all faulty!" he afterwards phoned to say in great agitation. "It will have to be repressed." Yet copies had already gone to journalists, the radio stations and other people, and there had been no complaint. But he refused to believe that there was nothing wrong with the disc until he was taken to my car and the whole disc was played through on the car CD-player with no trouble at all.

This phenomenon, for which nobody seems to have an explanation, is currently being investigated by at least one CD factory.

It occasionally happens that a disc is found to contain the wrong music, although the label is correct. This can happen in a CD plant at the end/beginning of a run when stampers are changed in the press, out of sync with the labelling machine. It is a human error and usually affects only one or two copies, so if you find yourself with one you have been very unfortunate. It will of course be replaced.

It is a sad fact that many of the CDs returned to us as faulty exhibit the causes of the fault only too blatantly as finger-marks and other dubious foreign matter of unknown origin. On one occasion marmalade was diagnosed. Many of the returned discs have obviously been maltreated and show not only finger-marks but scratches and blobs and other bits of dirt.

The microscopic information on a compact disc should be respected and the disc treated with care. Laser beams cannot pierce layers of human detritus.


If it contains the wrong music but is otherwise OK (correct label, booklet etc) please notify us by letter, postcard, fax, phone or email (for the respective addresses please refer to our home page), and tell us what you think the music might be ('a pop record', 'some organ music' or similar rough description). If you can, please tell us the matrix number stamped into the shiny centre area of the disc. Do NOT return the disc to the shop. You may, if you like, return the disc to us (and we may ask you to), but if you do, PLEASE SEND JUST THE DISC, NOT THE ACCOMPANYING PRINTED MATTER.

If you find yourself with a disc which doesn't play properly, or not at all, TRY IT ON ANOTHER CD-PLAYER. If it still refuses to play then please let us know, telling us the title and disc number, specifying precisely how it misbehaves ('refuses to play track x', 'skips a lot', 'machine refuses to play it altogether' etc). If you want to send it back to us please do so -- but again, just the disc, not the accompanying material. From the number we will be able to ascertain the factory where it was made.

A sizeable proportion of the CDs returned as faulty apparently have difficulty playing only the last track or tracks. This is generally due to an inadequacy in the player which prevents it from playing some of the longer CDs (75 minutes or more). Oddly enough this is often the case with some of the more sophisticated CD players; more basic, primitive ones seem to be able to cope perfectly well with the discs. In any case the failing is in the players, not the discs.

If you do find it necessary to complain about a particular disc please also include details about your CD player: make, model number and age. The factories often ask for this information.

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