MattF - very true. I admit I'd overlooked that Cu Ethernet is indeed galvanically isolated. Good post esp re STP/FTP grounding, though back to the why does it make an audible difference. Galvanic isolation effectively means DC is blocked/AC coupled; and the transformer sizes are optimised for ethernet high frequencies though some LF stuff will still pass through. I guess this is where this "isolator" claims its performance in "cleaning" up the LF "noise" other artefacts to be debated.

I am also reminded that I am incorrect re medical devices and isolators, this has nothing to do with measurement noise but is safety related as network devices are typically not medically approved (ISO13485) so addtional isolation is used via an approved isolator for compliance reasons.

G61R, 5K5's (fronts & centre), 5K's (sides & rears), D2500, JVC DLA-X70, QNAP, Roon(Pi)