If that were true, adding a switch between your router or NAS and streamer could not improve the sound. Yet it clearly does, IME.
Well it is Saturday evening and my dear wife will soon be home from a trip, so I will be brief :
I encourage people to look deeply at the actual methods being used--and what is accomplished or not--when considering various Ethernet switches and filters. And also to consider the goals.
Most of what is seen in various forms is strictly passive such as repetition of the multi-core magnetics that is already behind every RJ45 port in the world, plus a couple of capacitors and inductors.
Also popular are some attempts at improved clocking--though all but one company () does so only in a single domain and without any sort of true jitter reduction.
Yet it is important to consider what the goals really are--and I avoid speaking of "noise" in a general way as it is like going to doctor and ranting about "germs" or to a chef and chatting about "spices" in a generic terms. There are all sorts or noise--coming from everything, the chips themselves, the power networks on the boards, through the cable, etc. Some is common-mode, some is high-source impedance, and the frequencies are all over the place.
But how it all propagates, and how/why it has any effect inside the DAC, is a complex subject.
Our paper that Tom linked to above is our second one--more about clocking issues--but it does help explain how amplitude modulation (noise) turns into phase modulation and back.
For a dive into the multiple ways ground-plane noise (which essentially becomes what we refer to as "clock threshold jitter" affecting the DAC's master clock pin) propagates and methods to block it, please look to this paper:
"How perturbations on digital signals can affect sound quality without changing bits..."
[We take an active approach to it--and our EtherREGEN is still the only switch in the world putting Ethernet signals through high-speed differential isolation chips across an air-gap "moat" with dual-domain reclocking using 10GHz-capable ultra-low-jitter flip-flops.
Lot's of other fancy looking boxes out there--at prices below and way above us--but not much actual new technical innovation being implemented. Just sayin'...]
My point--and purpose to the links--is that we hope people will explore and educate themselves about the mechanisms that are actually taking place. Otherwise, without some shared technical knowledge and vocabulary, we are all just yacking generically in circles.
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