skin effect is real. I see proof of it every day as a tech for AT&T. You can test tarnished cable and detect huge attenuation at high frequencies. It's easily explainable through simple physics: high frequencies by definition have very tiny wavelengths. Wavelengths of a fraction of a millimeter don't use the whole cable. Of course, our bandwidth is much greater than 20 to 20k....we use 5k to 750k, and there are systems with greater bandwidth than that. Of course, the proof is whether it sounds better. I pulled off one piece of "cheap" (relatively) Synergistic Research cable and put on a one meter Siltech RCA. The difference was clearly audible, even though I still had weakerr links in the chain. Frankly I was surprised, because I didn't expect improvement until they were all replaced. Siltech uses unobtanium in their better cables.