Good responses by all. Yes, I too was wondering about the 500K -- that seems unusually high, and I would imagine that parasitic impedances in the circuit could become significant relative to that value, at least at high frequencies. But more significantly, I suspect that Vett's capacitor experiment is most likely a good example of what Redkiwi was referring to when he said:
One of the problems in science is that when experimenting you need to assume certain variables are not relevant in order to observe the impacts of an experiment on what you believe to be relevant. You cannot screen out all other variables all of the time.
My guess would be that the differing results with the two capacitors were not the result of the different capacitance values (the variable being tested), but were the result of differences in the departure of each device from being an ideal capacitor. Dielectric absorption, ESR (equivalent series resistance), leakage, stray inductance, and other known and unknown parameters make every capacitor something other than a pure capacitor. Which is why it is fairly widely recognized that different makes of capacitor, of the same values, can sound different, especially when they are in the signal path.
Redkiwi, I certainly agree that digital cables can sound different in an audio system. It is fairly widely documented, both in
this paper and in threads at this and other audio forums, that 1.5 meters is an optimal length for cd transport to dac connections, and significantly shorter lengths will increase jitter by causing the round-trip timing of reflections from the dac input, and re-reflections from the transport output, to be such that the re-reflection would arrive coincident with edges of the original waveform. Of course, the degree of that effect would be dependent on the degree of impedance mismatch at both ends, as well as on the rise and fall times of the transport output, and the jitter reduction capability of the dac (if any).
Re skin effect, I haven't performed or studied in detail any analysis of its relevance to audio frequencies, but based on what I have read I would not disagree that it could be marginally relevant in some cable configurations.
I do still feel, though, that inductance and characteristic impedance are not relevant to analog audio interconnect cables of reasonable length, particularly in the bass region. When you say
If the characteristic impedance of the cable is below the output impedance of the upstream component then phase errors can get audible, particularly in the bass, and is a major cause of the belief that interconnects can be system dependent.
my feeling is that something else must have been going on to account for the differences your testing revealed. Of course, as I noted previously, inductance certainly can be expected to be a significant factor in a speaker cable (as opposed to an interconnect, where source and load impedances are much higher than for a speaker interface). And since characteristic impedance is a function of inductance (and capacitance), there may be an indirect correlation between speaker cable characteristic impedance and performance, but not in the usual sense of impedance mismatch resulting in vswr effects.
Regards,
-- Al
