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Re: Definition: "Gold CD"

In article <[🔎] 87af6azvsv.fsf@garfield.complete.org> you write:
>Mark Ciciretti <mciciretti@mail.dzn.com> writes:
>> Actually, there are Gold CDs.  If you look in Sterophile magazine there
>> are companies that sell pressed Gold CDs.  Basically the aluminum middle
>> layer is plated in gold.  Suposidately the gold coating makes a difference
>> in the sound.
>It cannot possibly, since the sound is digital.  Unless you are
>reading it incorrectly -- audio CDs have no error checking.  However,
>this almost never happens and if it does it would not be noticeable

According to a course on Error Control Coding I was on a few years ago,
audio CDs have quite a lot of checking and correcting.  The data is
processed through several layers of ECC before being played.  All other
things being perfect, it should be possible to drill an 8mm hole through
any point on a CD, and the player will be able to reconstruct the missing
data from the rest of the track.  (I don't advocate doing this, because
all other things are -never- perfect!)

The raw data off a CD is very noisy (e.g. a lot of dust comes into the
CD player on the surface of the CD); I think you'd -really- notice it
if there weren't any ECC.  If the error control coding can't cope with
the noise on a few samples, it'll interpolate.  If the error covers a
whole frame or two, the player will go as far as to mute the sound for
a few milliseconds (this is generally unnoticable).  The skipping and
repeating that you get with, for example, portable CD players happens
when the player can't read an extended section of the disk, but this is
really a last resort.

(Note this is all from memory, and the course was a few years ago;
I may have misremembered.)

As for the audiophiles, they just -have- to spend their time tweaking
their sound systems to get better reproduction (a bit like what most
of us do with our Debian systems).  Now that most audio reproduction
has gone digital and is essentially perfect, they're having to invent
things to tweak.


Charles Briscoe-Smith
White pages entry, with PGP key: <URL:http://alethea.ukc.ac.uk/wp?95cpb4>
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