🚀 go-pugleaf

Peter Clinch wrote in message <36753AE1.BFA1F49F@dundee.ac.uk>...
>Kit-pui Wong wrote:
>>
>> Some people with "golden ears" claim that there are great
>> differences between an original CD and its digital CDR copy.
>>
>> Is there any **theoretical** ground about the difference ?
>> In digital world, information on CD are always O's and 1's.
>> A digital copy of an audio CD should store the same stream
>> of 0's and 1's and therefore produce exactly identical
>> output.

>But you don't get 0s and 1s out of the replay chain, you get analogue
>waves.  It is *possible*, I think, for a CD-R to have different jitter
>characteristics to an original, and jitter alters the analogue wave you
>get out.

Jitter is one of those hocus-pocus words that people like to throw out when
they don't know anyting else to say. I've never seen a reliable listening
tests that nailed an audible problem with a CD player down to just jitter.
Analog bigots whine about jitter, and then turn a deaf ear to 10, 100, or 1000
times more jitter in their precious tapes and vinyl.


>Assuming a difference is there (and I'm not saying it is: I don't know),
>I'd think you'd need pretty serious kit capable of *very* good
>resoltyion to notice it.

Actually, measuring Jitter is not exactly rocket science. You just need a good
FFT. Most jitter that I observe in digital audio equipment is at such low
levels to be trivial, and its source is ususally due to something like a
crappy job of isolating the power supply from the signal-handling circuits.

CD transports have to remove relatively monumental amounts of jitter to work
at all. The major source of it is the fact that the bits come off a slightly
eccentric disc rotating at several 100 rpm. If jitter due to spacing of bits
on the disc were a problem, it would show up at frequencies related to the
rotation of the disc, and vary from point to point on the disc, as its
rotation speed varies. Doesn't seem to happen.