Hi everyone
I like this kind of discussion. It shows how important it is to have a discussion about tuning and optimisation. The interesting thing here is that 99% of what is discussed is true, even if there are opposiing opinions.
Do you hear differences between an audiophile network switch and a cheap switch for home networks. Yes and no, for two reasons. Firstly, because you want to hear it, especially if you're about to swap a $100 switch for a $5000 switch.
Secondly, because you listen to music for a very long time with good hi-fi chains and compare them again and again. It's easy to explain, and it works like any kind of training. You get better.
Think of it like tasting wine. At first it's hard to tell whether it's red or white when you're blindfolded. But the longer you study wine, the more you learn to recognise the differences and eventually you get to the point where you can really tell the grapes from which the wine is made very reliably.
However, it is easy to explain why the chain does play a role for some people. The cause of all this evil is the conversion from digital to analogue. If we could hear digitally, i.e. translate the zeros and ones in our head, then our head would be the D/A converter and would decide on the quality we hear.
But that is not the case. We listen to analogue and the DA converter in our music system decides what we hear. And like all components, a DA converter does not exhibit perfect behaviour. There are effects such as ringing, noise,... The digital signal is also not a perfect rectangle (voltage off = digital 1 and no voltage on = 0), but at least rounded at the corners and the edges have an angle that deviates from 90 degrees (the perfect rectangle).
Without going into too much detail, the DA converter must recognise when the zero becomes a one. Since the edges are not completely vertical and there is also analogue noise superimposed on the digital signal. The edges are not always recognised at exactly the same time. This sometimes throws the DA converter off course and leads to a tone sequence (frequency response) consisting not only of the digital signal, but also being influenced to some extent by dirt in the digital signal. There are of course many tricks to keep the signal as clean as possible. For example, by rebuilding the signal and removing dirt from it again before DA conversion, but even then mistakes happen. Depending on what the dirt looks like, you will hear it more or less, depending on the chain, the time of day, the number of interfering signals, mobile phones, WLAN and of course the listener!
Finally, a particularly "nasty" source of errors in DA conversion. Direct current, as used for PoE (Power over Ethernet), i.e. power supply via the mains. If a direct current component now reaches the DA converter, this shifts the edge detection (transition from 0 to 1) and the analogue music signal suffers particularly badly as a result.
I'm already looking forward to your replies.