[vorbis] Copy protected CDs (off-topic)

[Segher Boessenkool]

Dan Hollis wrote:
> 
> On Wed, 20 Dec 2000, Gregory Maxwell wrote:
> > Best bet is that they clock themselves from the media and CD-Rs clocking
> > output is very jittery. This will cause their output DAC to jitter around
> > 44.1k rather then playing exactly at it.
> 
> No CD players *EVER* clock themselves from the media.

Nah. All *extremely cheap* CD players clock themselves from the media.
Yeah OK, that's almost all CD players. They just don't have a large
enough buffer to compensate for varying CD movement speeds, and can't keep
that speed well enough controlled. They use a PLL or something alike to
keep the DAC clock "in sync" with the CD bit "clock", so it isn't _directly_
clocked from the media (which is obvious for other reasons, like ECC blocking).

> > Even decks which have their own clock and fifo, the jitter buffering may not
> > be sufficient, or the jittered signal could potentially leak through due to
> > poor electronics design and modulate the output of the internal quartz
> > oscillator.
> 
> Not likely.

I don't see a quartz oscillator being affected, either.

> Most likely, the CD-R is marginally readable in that particular player,
> and the CD player is having to compensate for missing samples by using
> interpolation and other means.

A lot of cheap CDR's are chock-full of biterrors, especially if a
not-all-that-great CD writer was used.

But the most-occuring problem with CDR audio CD's is clock jitter, like
Gregory mentioned. Look around on the web and you'll find some reports.
I believe there was a discussion on this on the mp3encoder list a few
months ago, as well.

Ciao,

Segher

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