While I can hear differences between my DACs, amps, tubes, and headphones, I haven’t tried to hear differences between cables, and I think I would find it difficult to do so. But I acknowledge that some people can hear differences, and perhaps, in some cases, even with ease. If one can hear a difference, should it be measurable? Yes it should. Our ears, in a way, are also instruments measuring the sound and gives the measurement to the brain for interpretation. If the ears can measure it, must be possible to measure by other means. So, if it’s measurable, can we measure it? Now this is the tough one. We should be able to, but only if we are measuring the right thing, and with enough resolution. The problem is that we could be looking at the wrong thing, or not measure it accurately enough, or maybe the tech to measure it just isn’t available yet. What I’m trying to say is that I think it’s a bit more complicated than just throwing a frequency plot or some other measurement in someone’s face saying “I can’t see it, so you can’t hear it”.