OK, before the loonies come out of the woodwork...... Yes, the clock is sent with the data, but it has to be extracted. Extracting it means that you need a phase-lock loop to do it. All PLLs will exhibit jitter. How much depends on a lot of factors.
In the case of SPDIF, because it was not intended for anything other than testing, the clock contains a lot of data-correlated artifacts. This type of jitter is worse, in terms of sonics, than Gaussian noise. Jitter has 2 parameters that are important: amount (usually expressed in pSec, nSec, whatever, or unit intervals) and its spectral content. You see jitter numbers thrown around in the same manner as you will see THD numbers. Without the harmonic distribution of the distortion, that number is not all that helpful. (Some harmonics are especially nasty, while others can be pleasant.) So, not only do jitter numbers do little, other than provide yet another misunderstood venue for forum food fight fodder, there is not much discussion on what it sounds like. The best way that I can explain how jitter sounds, well.....as someone pointed out, you know when you hear something with less. You do not actually hear the jitter itself. What you do hear it mucks things up in a subtle manner. The 2 things that you will notice when the jitter is reduced is that the bass is tighter and more defined, and that the top end is cleaner and smoother. Some DACs have additional circuitry designed to minimise these effects. Sometimes they work well, other times they work better on paper than in practice. An example of such is the blind trust some designers place in ASRCs. They will all "remove" the jitter, but do so by moving it around. (Please don't ask me to explain how they work.) The less successful ones perform poorly because the chip designers took too many shortcuts in the implementation of the mathematical functions inside the chip that do the hard work. They end up spreading the jitter out all of the place. I can think of one very widely used ASRC that is used in a lot of cost-effective "one box, lots of functions for not a lot of money!" units. Pat -- ar-t http://www.analogresearch-technology.net ------------------------------------------------------------------------ ar-t's Profile: http://forums.slimdevices.com/member.php?userid=13619 View this thread: http://forums.slimdevices.com/showthread.php?t=56425 _______________________________________________ audiophiles mailing list [email protected] http://lists.slimdevices.com/lists/listinfo/audiophiles
