Ponderous. That's the adjective that comes to mind so often when I visit audiophile sites and come across yet another tweak suggestion. Over the years, there have been many such nuggets... Ideas like using a battery to power devices to make them "sound better" in supposedly very significant ways. Switching mode power supplies in general are said to be "bad". USB carries with it significant noise so we should to buy certain "filter" type devices (Audioquest Jitterbug, Uptone Regen, etc...). Server computers sounding different using the same high quality DAC when there's no DSP processing applied to the actual digital signal. OS optimization tweaks "reduces jitter" and again "sounds better"... The possibilities are endless!
On a few occasions, there are nuggets of truth in some of these ideas. For example, yes there is jitter to be found in some circumstances (small but measurable amounts like with S/PDIF and HDMI). Yes, sometimes you can detect noise from computers situated close to a DAC. Realize of course, many times the "solutions" advocated do not necessarily fix the problem. For example, I have yet to see a situation where a fancy passive piece of cable can fix jitter. And more often than not though, the subjective advocate/testifier/witness appears to magnify the purported effects to such extremes in the hopes of drumming up interest in what really should be rather insignificant issues. (Why folks would do this will be left to the reader to decipher... :-)
Which leads to today's topic... Ethernet galvanic isolation.