Digital Drive Upsamplers, DACs, jitter, shakes and analogue withdrawals, this is it.

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Re: Your player already has fairly low jitter measurements

Posted by Charles Hansen (M) on March 16, 2007 at 07:34:43

In Reply to: Re: Your player already has fairly low jitter measurements posted by Christine Tham on March 15, 2007 at 20:19:22:

<< the Miller analyser is (I believe) based on Julian Dunn's J-test method. The problem is that this does not actually measure jitter, what it's measuring are artefacts associated with perturbing a sine wave with a 1-bit amplitude square wave. >>

Yes, I believe that the Miller analyzer does use the "J-test" method. This is actually a large-amplitude *square* wave that is overlaid with a 1-bit amplitude square wave of a different frequency. One big problem with this method is that it was actually developed to stimulate the worst-case scenario of jitter introduced by an S/PDIF (or AES-EBU) link. It therefore has virtually no application whatsoever to one-box players, as they don't use the bi-phase mark encoding that is susceptible to the signal used on the "J-test".

<< What I do know from examining a Sony XA777ES ... is that there seems to have been quite a lot of attention paid to reduce the effects caused by logic induced modulation, which is a major source of jitter, certainly more so than on a typical universal player. >>

While this may be true of a "typical" universal player, I can assure you that there are certainly examples of universal players tested by Stereophile where this was *not* true. And yet the measured jitter numbers do not correlate well with what would be expected by comparing the designs. I believe that this is a flaw with the test (or its implementation), and not the result of faulty analysis. We already have one data point that shows 100% variation in the results of the Stereophile test on the exact same machine.

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