bhaagensen;547919 Wrote: > > As I understand a TDR will get you a measurement of how clean the > signal is? Asking, since it has been hinted that the Touch puts out > "cleaner edges" (and therefore makes it more likely that the DAC > interprets the signal with greater precision). >
What the TDR does is measure the impedance of the output. If the impedance of the source matches the impedance of the destination (75 ohms in the case of S/PDIF) there will be no reflections. Anything along the line from source to destination that is NOT 75 ohms will cause a reflection. Its called an impedance discontinuity. This is not the same as the cleanliness of the edge. You can have a perfect impedance source which produces no reflections and still have "dirty" (noisy) edges or slow edge rates. Its much easier to get and measure clean edges than it is to get and measure the impedance of the system. The TDR doesn't actually measure the impedance, it measures the actual reflections in a system. For this test what you do is run the output into the TDR, which then drives a long cable with a known terminator at the end (75 ohm resistor in this case). The TDR shows the original signal and the reflections. If the source is perfect you just see the original signal. Any impedance discontinuities show up as reflections superimposed on the signal after the time delay of the cable. If you get no reflections you know your source is a perfect 75 ohm source. We KNOW it won't be clean because there is a RCA jack in the path which is not 75 ohms, so there is going to be at least THAT discontinuity, the TDR will show that as well as any others. John S. -- JohnSwenson ------------------------------------------------------------------------ JohnSwenson's Profile: http://forums.slimdevices.com/member.php?userid=5974 View this thread: http://forums.slimdevices.com/showthread.php?t=78736 _______________________________________________ audiophiles mailing list audiophiles@lists.slimdevices.com http://lists.slimdevices.com/mailman/listinfo/audiophiles
