Impedance mis-match?

Here's the response from MF...

most digital parts I know of are 50 ohms (or 100 ohms balanced) to preserve square wave edges. That said at these relatively lowish frequencies (low MHz) such a mismatch is unlikely to cause problems unless going into extremely long cables.
So nothing for your average home user to worry about.....
Very best regards,

Randy Bingham
Phoenix, AZ. 85076
National Sales Manager
Musical Fidelity LTD.

I am extremely happy with mine - my Bifrost has never sounded so good.

And remember - Don't shoot the messenger :-)

Perhaps sales people should ask somebody before offering written explanation.

Thank you kindly, noble messenger :-)

While Mr. Bingham is correct that a lot of digital signal applications involve 50 ohm parts and components and 50 ohm cables, that is irrelevant because S/PDIF is specified as 75 ohms.

Also, it seems that he doesn't recognize what the concern is. The concern is that signal reflections caused by the impedance mismatch will result in distortion of the signal waveform during transitions between its lower voltage and higher voltage states, and vice versa. If that distortion happens to occur around the mid-point of those transitions, the result is likely to be increased jitter (random timing fluctuations) at the point of D/A conversion within the DAC.

That is likeliest to be a problem if the length of the cable is in between being very short and fairly long, as Kijanki explained earlier. However, whether and to what degree a problem may occur is all somewhat unpredictable, because it depends on the happenstance of the unspecified transition times (risetimes and falltimes) of the particular signal, on the propagation velocity as well as the length of the particular cable, on the design and especially the jitter rejection capability of the particular DAC, on the degree of impedance mismatch between the cable and BOTH of the components it is connecting (there will inevitably be some degree of mismatch even when connecting a 75 ohm cable to a 75 ohm component, causing some degree of re-reflection of signal reflections caused by the 50 to 75 ohm mismatch at the other end, in turn resulting in multiple back and forth re-reflections), etc.

See this paper for further elaboration.

The bottom line, IMO: In any given setup there may or may not be a sonic issue resulting from this mismatch, but it cannot be considered to be a recommended way of assembling a system.

Best regards,
-- Al