Does the quality of a digital signal matter?

Paulsax - Jitter is a function of CD pressing quality, transport quality, digital cable quality, jitter suppressing scheme, electrical noise etc. It is a function of whole system. Even if we assume that amount of jitter is constant at given moment effects of jitter after D/A conversion are proportional to magnitude of the analog signal. Second page of Stereophile article (thank you Jea48) describes audible effects of jitter. They describe loss of detail and change in sound of instruments (harsh sounding violins) that might be effect of burying lower level harmonics in noise. Effects that they describe are often called "digititis".

Some people believe that as along as exact digital data gets to DAC timing doesn't matter. Try drawing sinewave on moving paper by marking predefined points (horizontal lines on paper to make it easier) in exact time intervals and then joining them. If intervals are not exact resulting sinewave won't be smooth - it will be jagged. Horizontal/time error got converted to vertical/value error.

Bob - Yes, error correction scheme will take care of most of the problems but used scheme (Cross Interleaved Reed-Solomon) can only correct 4000 bits of data (about 0.1"). If you have tiny scratch along the disk longer than 0.1" correction fails (only for this error). CDP won't try same sector again resulting in loss of sound quality. On the top of it transport might have poor tracking (skip track) because of CD vibrating, poor light reflection etc.

I like the fact that CDs surface can be re-polished (that's what our library did to all CDs). It tried to re-polish LP once but for some reason it didn't work.

In Jea48's linked article the implication was that the level of jitter was related to or at least different for different frequency levels of sound (presumably after the DAC). Someone straighten me out on this. It seems to me that the bit stream speed is independent of the bit content. If this is correct than should not the jitter be either constant of possible a function of the disc itself (like radial position or burn/pressing quality)?

Paul, you raise a good question, and I believe that the key to the answer is that jitter should be thought of as noise in the time domain.

As you will realize, an analog signal will always have some amount of noise riding on it, which causes its amplitude to fluctuate to some degree, in a manner which is to some extent random. That noise will typically consist of a great many frequency components, all mixed together. Essentially a mix of ALL frequencies within some finite bandwidth, with different frequencies having different magnitudes.

Similarly, the random or pseudo-random timing fluctuations that characterize jitter in a digital signal will have a spectrum of a great many jitter frequencies all mixed together. In other words, there may be slow fluctuations in the timing, that are of some magnitude, accompanied by rapid fluctuations in the timing, that are of other magnitudes.

Some frequency components of the jitter spectra can be data dependent, because a major contributor to the electrical noise that is a fundamental cause of jitter is the rapid transitions of transistors and integrated circuits between the 0 and 1 states, and vice versa.

BTW, re the references in your two posts to disk speed, radial position, etc., keep in mind that fluctuations and inaccuracies in the rotational speed of the disk (which figure to be far larger in magnitude than the electronic jitter we have been discussing) are, or at least should be, taken out by subsequent buffering in the transport's electronics.

Best regards,
-- Al

This is another one of those issues/questions that comes up now and then (like double-blind testing, differences in cables, etc), and gets talked about a lot for a while. The things that always seem true with the threads include: 1) very few people agree; and 2) people make fairly bold statements one way or the other (often without actual personal experience, e.g., having compared cables under *controlled* conditions)

If the question is "have you heard differences in the same system and same room, using transport A vs transport B?", my answer is "yes..definitely". (if one wants to "disagree or argue with what I experienced, that's a "dead-end" I see no point in going down) If you are asking "why?" or "how big a difference", or "is it worth it", etc...well, those are different questions.

p.s. While the question speaks of digital, the OP seems to forget (or not know?) that analog is involved in a CD player, at least one that is not using an external DAC.

p.s. I had another thought : )

It seems to me that, when it comes to audio, we clearly don't know everything yet !