Basically the test they are using is not the right test for this sort of device. That particular test is only suitable for a DAC which takes S/PDIF input _and_ uses the s/pdif signal for direct clock recovery. They may have been using Transporter in S/PDIF input mode, but even then, the result is not of very limited practical significance because it only gives a peak-to-peak value for data induced jitter in the s/pdif receiver *for a particular square wave signal*. If you want to learn more about the test they are doing (J-test), it is described in Julian Dunn's AES paper "Jitter and Digital Audio Performance Measurements".
These magazines really do a disservice when they present jitter as if it is "just a number". There is no way to have any idea what a number means unless you know where and how the measurement is taken and what units it is. If you are going to present jitter as a single number, the most reasonable one would probably be picoseconds RMS, measured at the clock pin of the DAC. You simply can't measure this at all with something like the Miller analyzer. However, with a modern high speed scope and jitter analysis software you can measure it very accurately, and this is IMO most useful measurement in terms of predicting audible jitter for real signals. The specs we give for jitter are measured that way, using a 10GS/s scope connected right at the input to the DAC (17 ps). We also specify the jitter of the oscillator itself (11 ps), and at the end of a 75R terminated cable driven by Transporter's s/pdif output (35ps). I have not detected any process variance in these figures, which is to say any variance is below the measurable limits (which is the case for the vast majority of measurable parameters we deal with). -- seanadams ------------------------------------------------------------------------ seanadams's Profile: http://forums.slimdevices.com/member.php?userid=3 View this thread: http://forums.slimdevices.com/showthread.php?t=33276 _______________________________________________ audiophiles mailing list [email protected] http://lists.slimdevices.com/lists/listinfo/audiophiles
