Keeping Your CDs
Playing Forever
Several years ago, a second-hand CD shop opened in our
neighborhood. Great, I thought. Now I can get a few bucks back for some of those musical
miscalculations that were cluttering up my listening room. I packed up a bundle of discs
and trotted over to the store to unload them
The clerk in attendance -- not the owner -- inspected the
discs minutely, staring at their surfaces like a jeweler checks out a diamond. Most had
only been played once or twice, but several were rejected out of hand for being scratched.
I could hardly see the infinitesimal blemishes, and proceeded to explain that they would
have no effect whatsoever on the discs' playability.
"Sorry," I was told, "we don't accept
scratched CDs." Short of telling her that I was the expert and she was an idiot, I
had little choice but to pick up these damaged goods and leave. I brought them back the
next day when the owner was there and sold them to him with no problem.
Scratches of certain kinds can disrupt a disc's playing, of
course, but they have to be fairly huge. CDs contain a lot of data redundancy, and players
have sophisticated error-correction circuits that allow them to replace fairly large
chunks of missing information. The CD standard requires that any player be able to ignore
a dropout 0.2mm long -- a lot of data when you consider the microscopic size of the pits
on a CD's playing surface; I've never encountered a player that couldn't handle a 0.5mm
dropout, and some breeze over 1.5mm dropouts or even worse. In theory, you could drill a
1/16th-inch hole in a disc and play it on such a machine with no problem. So the tiny
scratches that occur in normal disc handling are almost never audible.
But that's not to say a CD is indestructible; you do have
to exercise a certain amount of care if you want to keep your discs playing flawlessly
forever.
Major enemies are fingerprints on the playing surface. The
laser has to be able to penetrate them in two directions and stay focused on the metallic
surface embedded in the disc. Grease on the surface -- from fingers or any other source,
such as airborne kitchen grease -- can cause the laser to mistrack, and if this is severe
enough the signal will skip or mute.
The cardinal rule is to handle discs by their edges only
and keep them in their jewel boxes when they are not being played. This will also lessen
the chance of dust collecting on the surface.
If you do have to clean the disc -- and this should only be
needed very rarely if you're careful -- use a soft dry cloth or, if necessary, one of the
proprietary fluids designed for CD cleaning. And forget your instincts from the vinyl
days, when the proper way to clean a record was in a circle, going with the grooves. With
a CD, the cleaning cloth should go radially from center to edge or vice-versa, or even
straight across. Never wipe around; this can result in microscopic circular scratches that
can play havoc with the laser beams ability to read the data.
When you take a disc from its jewel box or put it back,
make sure it doesn't brush against the spring-loaded center mount -- that's a major source
of scratches. And store the boxes on edge rather than flat. The discs are supported in the
middle only, and if laid horizontally, the edges may eventually droop, especially if the
discs are exposed to heat -- and it doesn't take much. Things aren't so bad at home in
this regard, unless the discs are stored in direct sunlight, but cars in summer are very
hostile places for discs.
Always keep your CDs in their jewel cases and keep the cases
stored vertically. |
If the disc does become deformed, pitch it. It almost
certainly won't work properly, or at all, and may damage your player.
Oddly enough, you should take great care with the label
side of a CD. The "playing side" is really just a transparent plastic disc; the
actual data is pressed onto the label side, where a coating of reflective aluminum is
plated on it, and then a thin layer of lacquer applied to seal it in. The label is
silk-screened onto the lacquer. Any damage to the lacquer will eventually let air reach
the aluminum, which will begin to oxidize. Eventually it will become so cloudy that it
will no longer reflect the laser beam and the disc will be useless. The condition is
sometimes called "laser rot."
While there were reported cases of spontaneous oxidation in
the early days of the CD, they were extremely rare. The rot is much more likely to be
caused by something you do. A scratch on the label side may penetrate deeply enough to let
in air (that's very unlikely on the much thicker playing side), and markers used to
inscribe your name can be deadly, as can some cleaning solutions and the adhesive on name
tapes. Flexing a disc can cause tiny cracks that will eventually cause problems as well.
Occasionally, some "expert" will suggest you can
improve your sound by some unlikely means, such as freezing a CD or painting its edges
with a colored marker or adding weighted rings around the circumference. Don't waste your
time or cash -- all but the most deranged audio gurus agree that these make no difference.
Compared to the LP, the maintenance regimen required for
CDs is pretty straightforward and low-intensity. But it is important, and you ignore it at
your peril.
...Ian G. Masters
ian@mastersonaudio.com
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