I seem to be quoting this ex-Microsoft guy [a co-developer of, among other things, technologies used in HD DVD], below, more and more. . . . Huh, maybe he is finally starting to see the light?
"While differences still show, they are so, so down in level as to not ever be an audible concern. . . .
So as usual, we can show measurements that bother the eye but not the ear.
For the first time anywhere, we have shown that we can change the analog output of a DAC by changing how we feed it in digital domain in USB. Shorter cables provided improvements that were visible. Alas, two other factors conspire to make this non-news:
1. Schiit Modi 2 that I have tested is horribly designed. It is sensitive to both USB power and data noise. Even a cheaper DAC like Behringer shows that such sensitivity is due to poor DAC design than anything to do with USB cables. The Behringer performance is better than Schiit with any cable and shows no need for tweaking the USB cable.
2. I have hugely magnified these differences. Without this magnification, the differences even with lousy DACs like Schiit are literally in the noise.
So nothing here explains the fantastical subjective differences people report between USB cables. I suggest those people conduct some blind test to get to the truth of whether they are hearing any differences especially if they are using better DACs than Schiit Modi 2."
Source: "Do USB cables make a difference?"