tonyptony;487812 Wrote: > > Sean (or John S. or Phil L. if you've measured it), what is the output > return loss from the Touch SPDIF? And, if the numbers are available, > over what bandwidth?
I'm not an expert on RF measurements but I doubt if that is a good metric per se for s/pdif performance when we can observe jitter directly. For example, we already know that RCA connectors have issues but that is really a minimal factor compared to things like the oscillator's noise and the particular design's s/pdif transmitter circuitry. However, do check out ar-t's TDA measurements which are really interesting. The tests I usually did were with a Lecroy 64xi reporting RMS variance from an ideal time interval, in a few configurations: 1) to measure the internal oscillators and to look for the added jitter as signal passed through logic gates (prior to s/pdif encoding), I would use the standard lecroy probe with a modified bayonet tip, having a minimal ground lead. This is where we get figures like "11ps at the oscillator" or "17ps at the DAC" for Transporter. 2) to measure the jitter of the s/pdif signal I would usually use an RG6 cable with an RCA crimped directly on one and and a BNC crimped directly on the other end. The RCA goes into the Squeezebox and the BNC goes into a tee with a terminating resistor right onto the scope input. The Lecroy has the ability to recover a clock from an arbitrary data signal. This is where we get figures like "50 ps at the DAC". 3) there is another test that is interesting which is to feed an s/pdif receiver chip and look at the MCLK coming out of it. Sometimes I would do this with Transporter's outputs looped to it inputs. I did not spend a whole lot of time on this but it was an interesting way to see the total performance difference between the various media. If anyone actually has a high-end scope and would like to try these sort of tests I could provide more guidance on how to do it. I think it's a shame that everyone seems content to speculate about jitter while so few people actually test it. -- seanadams ------------------------------------------------------------------------ seanadams's Profile: http://forums.slimdevices.com/member.php?userid=3 View this thread: http://forums.slimdevices.com/showthread.php?t=71464 _______________________________________________ audiophiles mailing list [email protected] http://lists.slimdevices.com/mailman/listinfo/audiophiles
