USB cables and Galvanic Isolation

I've made up my mind that I will try a better quality cable.  No harm, no foul.   
Except the question is which one?  
Any max. length as far as usb cables go?

Hopefully Dow Jones will not report this one and get it deleted:

Length does not matter, but preferably short. About 1-1.5 meter no longer, if your equipment proximity allows. 50 cm would work well too.

As for which one, depends on budget. Examples: entry level Wireworld, AQ, Triode Wire Labs, Supra, Sablon

I've tried Kimber and didn't notice a difference of course I had my wife switch between the expensive and generic cable to eliminate bias. Try the DH Labs you mentioned.

Why is galvanic isolation so important? I know what the definition is.
What does it improve? Why isn't it used all the time. Galvanic action, is growing barnacles, isn't it? To galvanise, is to Zinc plate iron, right?

So what is galvanic isolation?

Just wondering?

Regards

USB of newer DACs is asynchronous, meaning incoming data clock and D/A conversion clock are independent.  Sound cannot be affected by the timing of the data, as it is with S/Pdif,  but still can be affected by injected electrical noise (that affect internal DACs clocking).  To limit amount of this electrical noise,  cables with data lines only (no power) are better, when power is not required (DAC has own supply).  Good shielding also plays role to limit ambient electrical noise pick-up.  Galvanic isolation separates two circuits electrically to prevent current flow between them.  It can be done with transformers or optocouplers, but in either case it is not perfect, since there is always very small capacitance between two sides of galvanic isolation, allowing very high frequencies to pass thru.  Nothing is perfect, but galvanic isolation eliminates most of electrical noise.  Another good step would be to reduce noise on the source (computer) side.  That might be difficult since some computers have horrible power supplies.