Digital Coax Cable - Does the Length Make a Difference


Someone (I don't remember who) recently posted something here stating:
"Always get 2 meter length digital cables because I have experienced reflection
problems on short cables, resulting in smeared sound and loss of resolution."

With all due respect to the member that posted this, I'm not trying to start a
controversy, just wondering if others have experienced this.  

I will be looking for a Digital Coax cable soon to run from my Node2i to a Dac.
I really only need 1/2 meter. Not sure if a short cable like this is a problem or 
just a case of Audio Nervosa.  

ericsch
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.