"John Phillips" wrote in message
...
On 2007-05-23, Serge Auckland wrote:
"Steve Swift" wrote in message
...
What plausible causes exist for the audio being different when the
individual bits being read off the CD are not? They may arrive with
subtly
differing timings, but the sequence is identical. I'm sure the timing of
the bits varies every time a CD is played, due to varying rotational
speeds of the CD.
If you can do a double-blind test, and he can do this reliably, then you
have something. The only mechanism I can think of that could *possibly*
account for sonic differences is if the copy is so poorly burnt that the
CD
player has a hard time reading the disc and there's a lot of
interpolation
going on. It would then be useful to repeat the DBT using another CD
player
of competely different type to see if the same results are obtained.
Otherwise, two bit-identical CDs will necessarily sound the same.
A common audiophile postulate for audibility of different discs of
nominally identical material is "jitter".
This surprises me a little, having looked at some AES papers on the
audibility thresholds for jitter. Although the research does says that
audible jitter at 10 kHz and above is remarkably low.
Also it seems to me that the jitter hypothesis relies on inadequate
engineering of clock extraction circuits to allow enough jitter to get
through to the audio output. Quite possible I suppose, but eminently
curable (and should not happen in the first place).
--
John Phillips
Quite so! There's no excuse these days for jitter. However, this doesn't
seem to have got through to some designers of "audiophile" DACs. One DAC I
saw reviewed (I can't remember which one but it was expensive!) made the
comment that it was so sensitive, it would reveal the differences between
digital cables. What this meant was that it had such an appallingly
engineered receiver that there was no reclocking of data, and pattern jitter
on the cable went uncorrected. So much for "so sensitive", crap actually.
S.
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