[Dixielandjazz] Fw: CD question

[Andy.Ling at Quantel.Com]

Bob Romans asks :-
> Have you ever had someone tell you that your cd's would
> not play in the cd player? 

There are several reasons for this. The CD is read by shining
a laser at it and looking for the reflections.

Originally CDs had a nice shiny silver surface with small
indentations for the "digital" bits. The difference between
these two areas was large and so was "easy" to see.

When writable CDs came along the colour was changed. Some
were gold, some green, some even still silver. Also the
indentations became holes burnt by the write process. All
this made it more difficult to read and sometimes a more powerful
laser was needed. Most CD players could cope, but some didn't

Then along came re-writables. These use a different technique
again which makes it even more difficult to read. The upshot
of this was that most audio CD players couldn't read them.

Newer CD players are now designed to cope with CD-Rs and CD-RWs

Another factor is that the laser slowly degrades. As it gets
older it loses its brightness. I have a CD player which is
1983 vintage. It stopped playing some CDs. When this first
happened, a tweak of a "brightness" control fixed it. The next
time it needed a new laser. It now needs another laser and
has been retired.

DVDs pack the data in tighter. To do this they need a smaller
beam of light to do the reading (amongst other things). This
is partly achieved by using a different colour laser. A CD
player will not even come close to reading a DVD.

If you are producing CDs for others, then commercial pressings
will work for 99.9% of people, but obviously have a high
initial cost. CD-Rs will work for most and are cheapest for
low volume production. CD-RWs should only be used if you
really do need to make changes. Even then it is probably
easier to just create a new CD-R


Andy Ling