Question about length of SPDIF COAX interface cable length

Hi,

Not sure why this is the case, but I spent quite some time switching between my 8" cable and 1.5M cable. For some reason, I am finding myself preferring the sound of the 1.5M cable, where the 8" cable seems to sound a bit too bright.

Yes, the 1.5M particularly for SPDIF/COAX, DACs, etc. As already noted, and several references around about reduced reflections, and how reflections can sometimes be somewhat attenuated by the longer cable's added capacitance depending on the cable design used.

I tried it with .5M, 1.0M, 1.5M cables on my own DAC and prefer the 1.5M as well, fwiw. You already figured it out...   

That's surprising.  Brightness would suggest a presence of the jitter (that translates to added noise).  What about clarity/transparency and imaging?  It is remotely possible that some electrical noise is injected from the source, possibly thru the shield, while longer cable, having more shield inductance, impedes electrical noise injection more, but I'm grasping at straws.  Did you keep both gear pieces in the same physical location for both tests?  Did you notice it at the same time of the day?  Often people experiment after work and dinner around 6-7PM, when radio stations power is suddenly reduced by FCC regulations (better signal propagation at night).

I tried it with .5M, 1.0M, 1.5M cables on my own DAC and prefer the 1.5M as well..

I would also pick 1.5m from these choices.  8" (0.2m) shouldn't have reflections at all (not a transmission line).

grm,  I assumed typical 25ns transition time, but perhaps it is different.  Maybe your source is swinging faster, especially at smaller capacitive load (shorter cable).   Whatever it is - ears are the best judge.  Same goes for different 1.5m cables - cheap cable can have by chance better impedance matching with your gear, than very expensive one, resulting in better sound.