This is what I say on every forum. The jitter of the digital source is MORE IMPORTANT than the DAC. It's true. And Empirical Audio has been developing lower and lower jitter products for more than 15 years.
You must understand what jitter is and how it should be measured if you want to make intelligent decisions. A single RMS or even peak-to-peak jitter number is grossly insufficient. If you purchase gear based on such specs, you are making a gross error. The first flag that everyone should raise with a product is if they claim to eliminate jitter or have zero jitter. Impossible.
Jitter occurs as a Gaussian distribution of cycle-times. If you only publish one number, you don't know the shape of the Gaussian curve. It could be wide a flat or narrow and tall and still have the same RMS jitter number. The "tails" of the jitter distribution are also important. If these P-P maximums only occur every 20-30 seconds, this is totally inaudible. At Empirical Audio, we measure the jitter distribution in a histogram. We have found that narrow and tall distributions sound much better than wider, shorter distributions, even if the majority of the jitter is in the 50psec range. This makes perfect sense, since the jitter of a thin distribution is bunched in a tight range and not varying widely on average.
Steve N.
Empirical Audio