This article is from the rec.audio.* FAQ, by with numerous contributions by Bob Neidorff others.
Some recordings are better than others. Some artists are better
than others. Some recording engineers are better than others.
Some microphones are better than others. Some music is better
than others.
Ignoring that, there is some difference between discs. Some
of the very earliest discs were badly made and deteriorated
with time. The technical problems that caused those problems
have been solved.
Some "gold" discs are available which are advertised to have
better life and quality than common "aluminum" discs. These
sell for an extra US $15 or more per disc over the cost of the
same music on a common disc. Studies have shown that there is
an advantage to glass-encased, gold platters for archiving
computer data that is not error tolerant and will need to be
stored for many tens of years. I have yet to see a similar
comparison which justified any extra effort for storing audio
recordings for 50 years. Part of the reason for this is that
audio recordings contain error correction codes, allowing a
CD player to perfectly reconstruct minor flaws. Another reason
is that CD players can effectively reconstruct badly damaged
audio data, even if some data is completely missing.
Some discs seem to have pinholes in the aluminum, which are
visible when the disc is held up to a strong light. However,
these discs play fine and last very well, so the effect of these
pinholes is probably nil. Some have performed studies counting
errors on various discs with various players. They found that,
in general, the error count was consistent from one player to
another. Also, in general, most discs have a low, consistent
error rate which is perfectly correctable using the redundant
data stored on the disc. This study did find that one group of
discs had a higher error rate than all of the rest. This group
was the promotional discs, also called "music samplers" given
away by music companies to introduce you to their family of
artists and performers. Despite these higher error counts,
these discs still played fine.
If there is no abusive handling involved, I have rarely heard of
a disc that degraded with time. Of the few that have existed,
they tended to be from one of the bad batches mentioned earlier.
There is no doubt that some discs are mastered better than
others. Some are badly mixed. Some are so badly recorded that
there is noticeable clipping. Some are made from damaged master
recordings. CD technology is no guarantee of good music or of a
good recording.
 
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