USB cable

Solid core cables are best for USB.  All Audioquest cables ae solid core, for ex.  Silver helps too.  A Hong Kong ebay advertiser of solid core silver USB cables made one up for me that is a great performer.  

I had been experimenting with USB cables and was shocked at what a difference they can make, especially if you have quality components at both ends.

Contrary to what @kijanki writes, even if your DAC or USB board is self powered you MUST have the ground connection (pins 4) connected or it will not work. And ONLY the data?

@melm  I thought it should work, since it is differential signaling (receiver detects the difference between +data and -data lines.  Receiver ignores any common mode (including GND reference).  Many people lifted GND (cut GND wire) and reported improvement in sound, but it might not work if system uses Single-Ended signal for handshaking.  Easy to try with cheap plain cable.  I will read more.

USB cables made no difference in some systems and huge difference in others.  It can be attributed to the type of the DAC.  When DAC is synchronous cable can affect timing, but with asynchronous DAC timing is not involved.  Better shielding plays role, but very expensive cable doesn't have to be better - try before you buy.

You almost always will need the ground as the common mode range of the differential transceivers is rather small.

Audio2design - It makes sense.  Thank you.

There are people who lift the ground after handshaking takes place.  Others install a small resistor in the ground line.