12-18-14: Geoffkait
I also do not happen to think the dielectric material affects the velocity of the signal. As I already said I think the velocity of the signal is fixed (constant) for a given medium, I.e., copper or whatever.
That is not true, Geoff. What Kijanki said is correct. For starters, see
this Wikipedia writeup. Many other references can be found which will further confirm this. Widely varying propagation velocity specifications for various cables utilizing copper conductors can also be found.
12-18-14: Jea48
An experiment for those of you that use a CD transport and a separate DAC. If your digital coax cable has a solid core center conductor try this experiment. First listen to a good sounding CD with a strong female voice. Find a particular track you like and listen to it closely a few times. Now flip the digital cable end for end and then listen again. One good CD that comes to mind is, Etta James "Love Songs" track 1) "At Last". Also try a good sounding CD with a piano solo. Post back your results.
I don't use a separate DAC, but FWIW I can hypothesize a reason why a symmetrically designed digital cable may sound different, under some circumstances, depending on the direction in which it is connected. My hypothesis, though, has nothing to do with the wire itself having directional properties, and says nothing about the possibility that a symmetrically designed cable conducting analog signals may be have directional properties.
The connection between a digital cable and its connectors will have an impedance discontinuity and inaccuracy to some non-zero degree, which will result, to some non-zero degree, in some fraction of the amplitudes of whatever RF frequencies it may be asked to conduct being reflected back toward the source of the signal. I would expect the magnitude and character of that impedance discontinuity to not be totally identical at the two ends of the cable, due to small differences in solder application, crimping, etc., and perhaps even to dimensional tolerances in the connector.
Also, the output impedance of the component driving the cable and the input impedance of the component receiving the signal will not be precisely accurate.
Therefore the impedance mismatches between the cable and each of the connected components will differ depending on which end is connected where. And digital audio signals contain frequency components extending well into the RF region, up to at least tens of MHz. (Keep in mind that the risetimes and falltimes of the signal contain significant frequency components that are much higher than the clock rate and the data rate).
Depending on these factors, and also on the length of the cable, and also on the data rate that is being transmitted, the resulting reflections may very conceivably affect waveform quality at or near the mid-point of positive-going and negative-going transitions of the signal, those transition mid-points being what the receiving circuitry responds to. Degradation of those parts of the waveform will affect jitter, and therefore potentially sonics, to some degree. And that potential degradation will, per the earlier parts of this explanation, be affected by which connector is mated with which component. It will also be affected by whether the more significant of the two potential mismatches is at the receiving end or the transmitting end, and by the degree of impedance mismatch at both ends (which will affect how many back and forth re-reflections occur until their amplitude becomes insignificant).
See
this paper for further discussion of the effects of impedance mismatches and waveform reflections on jitter, although the paper does not address the question of directionality.
If all of that sounds a bit far-fetched, IMO it is less farfetched than an assertion that wires themselves have directional properties to an audibly significant degree.
Best regards,
-- Al
