From a post by member Kirkus (who has a vast amount of hands-on experience with the internal workings of CD players) in this Audiogon thread from 2011:
Regards,
-- Al
Two big conceptual errors I see very commonly are the assumption that any intrinsic jitter related to retrieval of information off of a CD actually occurs through the forward signal/data path, and that any sonic artifact associated with parts upstream of the DAC must be classifiable as jitter.
In reality, CD players, transports, and DACs are a menagerie of true mixed-signal design problems, and there are a lot of different noises sources living in close proximity with susceptible circuit nodes. One oft-overlooked source is crosstalk from the disc servomechanism into other parts of the machine . . . analog circuitry, S/PDIF transmitters, PLL clock, etc., which can be dependent on the condition of the disc.
One easy way of measuring this on the test bench is to have two versions of the same test-tone CD, one pristine, the other scratched. A conventional distortion analyzer is used to null out the the tone(s), and then an FFT (or visual 'scope analysis) is used to analyze the residual. One would be surprised at some of the nasty things that sometimes come up out of the noise floor when the focus and tracking servos suddenly have to work really hard to read the disc.
Regards,
-- Al