[vorbis] Copy protected CDs (off-topic)

[Gregory Maxwell]

On Wed, Dec 20, 2000 at 03:06:14PM -0800, Dan Hollis wrote:
> Because it has to be converted to a glass master for pressing, which is an
> expensive process. It's absolutely NOT because it's 'more accurately
> sampled'.

I don't think he was refering to the actual sampling process, but insted to
the process of cutting the bits onto the master.

The CDR does have a pre 'groov' etched in which is invisible to normal
drives and durning burning, but as I understand it, it doesn't actually
control spaceing to the bit 'duration' level. The CDR still drifts.

You can see this drift on a CDR very easily: Create a CDR with pulses at a
1khz rate, hook a wideband scope to your cd player output and attach a high
accuracy 1khz source (a desktop lab time source is useful here, a 1MHz out
from a survey grade GPS into a down convery would probably work) to the
trigger.

Watch the pulse dance around.

The devices used to etch glass masters have thermally stablized high
accuracy clocking sources, there is nothing like that in your typical CDR
drive.

All CD drives are buffered, they must for Ecc.. However, many (most?) are
still globally clocked by the disk. They only care about whole bit level slips,
but much smaller amounts of jitter being pumped into the DAC clock can be
heard by human listeners. 

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