If you have noise or degradation or timing issues, it (correct me if I'm wrong please Greg) is going to result in pops, dropouts, and jitter.
If the level of noise is significant enough to distort the digital waveform only (see here: http://lampizator.eu/LAMPIZATOR/TRANSPORT/CD_transport_DIY.html). The noise that is of concern is at a level low enough not to affect the digital signal, but high enough to affect the analog components. The main issue there in isolating that noise related, on the one hand, to the availability of components (ie: transformers, chips) that could isolate noise from a USB source while still allowing full USB 2.0 speeds (Schiit found that network isolation transformers work well for that) and on the other hand, removing noise generated by the USB components themselves.
I still don't understand why you chose to pull me up on that but not theorist,
You "pulled up" theorist very well, and for the most part, I agree with your responses to him. I don't need to duplicate that. Going by my own experiences, I don't believe that he may not have experienced a difference between USB cables, but what he attributes that to is wrong to me as well. The difference is that I know of perfectly reasonable, technically sound reasons why he (and other people) may have experienced what they have.
The two main problems I see here are, respectively:
1. Someone believes they have a difference swapping a cable. Instead of asking "Why is this happening? What don't I understand about electronics that would be useful that I could improve my system without expensive and unnecessary trial and error?" they may end up arguing with incorrect assumptions as theorist did.
2. Someone else believes that the first person's experiences are BS, but instead of asking "Why are they experiencing this? What could be a possible technical explanation if what they are experiencing is genuine?" they end up arguing from the point of view of their limited knowledge.
The irony is, I now know two companies who, respectively, solved pretty much all analog and digital cable issues using basic electrical knowledge. One I've already mentioned.