Digital Coax Cable - Does the Length Make a Difference

I was aware of the explanation for S/PDIF.  I’m curious if the same applies to USB and other digital implementations.  I would assume yes.  Jaytor of Kijanki?

I was aware of the explanation for S/PDIF.  I’m curious if the same applies to USB and other digital implementations.  

No, I would not expect the guidelines for optimal S/PDIF cable lengths to apply to USB.  For one thing, modern USB implementations (i.e., those operating at 480 megabits per second and higher) have far faster risetimes and falltimes than S/PDIF (or AES/EBU), which operate at vastly slower bit rates.

FWIW I don't recall ever seeing meaningful information as to what cable lengths for USB tend to be more optimal than others in audio applications, if it makes any difference at all.

Excellent answers by Kijanki and Jaytor to the original question, BTW.

Regards,
-- Al
 

Shorter USB cables will not be a problem. The biggest difference is that the USB clock is not used to generate the DAC sample clock on modern DACs, so any jitter introduced by reflections from the connection will not cause DAC clock jitter. 

That's not to say it will not have any impact since it can contribute additional noise, but it's likely that other noise transmitted through the USB connection will have a larger impact. And a longer USB cable provides more opportunity for noise to be picked up in this connection. 

Any optical cable that is lower cost (under $50-60) is going to be made from monofilament plastic.  While these are okay, they do also have a loss of high frequency resolution.  If you use optical, you really want a glass fiber cable.  These are definitely more expensive.  The best for the money is always going to be Lifatec ($120 / 3 feet,  or any custom length).   There are other more expensive otions (Wire World Supernova 7, DH Labs Glass Master Toslink, etc.).