I have done tonnes of tests with friends involving different USB cables and the didn't know which one they were hearing.
Sometimes for both tests you can use the exact same cable and my friends have claimed one sounds very different from another. It is all in your head. You need to understand how a conductor works first of all, then you need to realize that anecdote is worthless in the face of objective fact. Open up a $5.00usb cable and a $50.00 USB cable and you'll see they are all just copper. If you think digital cables can make that much of a difference, buy audiophile sata cables, audiophile harddrive, etc.
USB cables effecting sound signature is theoretically and physically impossible as long as they are up to spec.
Indeed, it seems that if you can hear a difference between 2 (USB) cables, it's because one of them (even if it is the premium cable) is almost certainly doing something horribly wrong and altering the signal unacceptably.
Edited by dclaz - 10/18/13 at 1:34am