None of the tests in this thread actually measure jitter. What they do is run a test signal through the device and hook the analog outs up to a spectrum analyzer and look at the sidebands around that test signal.
THEN they work backwards and say what jitter would be required to generate those sidebands. Everyone of these uses a very simplistic model for jitter->sidebands so their calculation of what jitter would result in a particular spectrum can be quite inaccurate. In addition they assume that ALL of those sidebands were caused by jitter. There are MANY ways sidebands can show up in audio gear other than jitter. Leakage of noise from the power supply can easily produce similar results. As can an electronic light dimmer in the room tests are being performed in! I'm not saying that any of these are true in this case, just that its very hard to make absolute pronouncements from these types of tests. I've done some experiments with these tests and compared them to real jitter measurements of clocks in several DACs and frequently find large disparities. For example one DAC came out to about 65ps when measuring the clock feeding the DAC chip, but when measured using this type of test it came out to 350ps. These tests are somewhat useful for comparing between devices WHEN the same test equipment is used and exactly the same methodology is used in both cases. Any change in methodology or equipment pretty much invalidates even this. Jitter is a very complex subject, reducing it down to a single number and using that for comparison between different devices is fraught with peril. ESPECIALLY when using tests such as these that are not actually measuring jitter. I had an interesting test on this years ago. I had a DAC for which I made two different input receivers. One produced a "jitter number" of 75ps and the other over 250ps. (measured at the clock input to the DAC chip) The 250ps one sounded much better! It turned out the characteristics of the jitter were radically different and that turned out to be far more important than the ps number. John S. -- JohnSwenson ------------------------------------------------------------------------ JohnSwenson's Profile: http://forums.slimdevices.com/member.php?userid=5974 View this thread: http://forums.slimdevices.com/showthread.php?t=84999 _______________________________________________ audiophiles mailing list [email protected] http://lists.slimdevices.com/mailman/listinfo/audiophiles
