How can different CAT5/6 cables affect sound.

Once, one of those I-trust-my-ears guys was going on about how he didn’t like the sound of fibre Ethernet cables:

He claimed they sounded "glassy".

Glassy as in... fibre? Fiber? Fiberglass?? You can’t make that up.

@retiredaudioguy to answer your question, no, you are not missing anything - any components, cables, tweaks, etc. in the Ethernet chain (that is, everything upstream of the network streamer) have zero bearing on sound quality; because, as you correctly stated, the TCP protocol itself is error-free.

So error-free, as a matter of fact, that your streamed music travelled thousands of miles from Qobuz or Tidal servers, through countless data farms from which twee audiophile accoutrements are conspicuously absent, yet arrived at your home thoroughly unscathed and without a single bit out of place.

It is still advisable to use SFP (fiber) for the last run of cable into the streamer, to ensure proper galvanic isolation of the audio system.

At the risk, of course, of making it sound "glassy"! 😂🤣🤣

Statistically, an Audiophile is more likely to experience a Marian apparition than an Ethernet-related SQ improvement.

Anyone who holds the mistaken belief that cables supporting TCP transmissions, routers, network switches and the like can make a difference in sound quality should be required to read the following before opining further:

http://units.folder101.com/cisco/sem1/Notes/ch7-technologies/encoding.htm

Followers of the "all-digital-is-analog" superstitions won’t likely read past the first page, so the TLDR is that TCP protocols guarantee error-free data delivery regardless of the vector on which it’s transmitted, thereby effectively abstracting the physical layer.

That said, copper cables transmitting TCP can indirectly affect sound quality by hosting parasitic noise. As others have confirmed, this is easily solved by using SFP (fiber) in the last run of cabling going into your streamer. This prevents any ground noise from reaching your system by galvanically isolating it (fiber is non-metallic, therefore non-conductive, therefore it does not pick up or transmit EMI or RFI).

Best practice is to keep all Ethernet gear in a utility closet / room at a remove from the listening room, wall warts and SMPS-powered computers and what not included (keep them on a separate AC circuit from your system), and run SFP fiber from your switch to your streamer. This way what happens in the utility room stays in the utility room, and inky black noise floors are yours.

Instead of retreating to the same old refrains, try to find explanations for why individuals hear differences with a multitude of audio streaming devices.

@sns 

In many instances, those differences are heard in systems that are not galvanically isolated behind at least one run of SFP fiber.

When differences are still heard with components or cables located upstream of fiber isolation, explanations still exist for that phenomenon, to the extent that psychology is indeed a science.

@sns 

Tedious as these threads are (here we agree), they exist because some folks keep spouting nonsense, rooted in ignorance and false superstition, as fact.

Come to think of it... Oh, never mind.

Until these folks either start educating themselves or stop posting, I am afraid these discussions will continue, even if, like you, I’d rather they didn’t.

@steakster thank you for posting this link, it illustrates my point.

Didn't know you were allowed to straight up hawk your stuff on What's Best Forum. Maybe you have to be a VIP donor?