It’s a digital DATA, but it is streamed through the LAN by an analog electric current.
The DATA is channeled through JR45 cables that react to RFI like antennas.
And all the devices of the LAN who are not powered by a LPS spread high frequencies of electrical noise all over the LAN (modem, router, computers, switches…).
All these interferences reach the endpoint with the DATA, and degrade the SQ.
An optical isolation right before the endpoint eliminates them all. The analog electrical current of the DATA is converted to light, while the interferences and noise are filtered because they don’t contain DATA.
I use $40 conerters from Amazon, and they clearly improve the sound.
It’s important to power the second converter, the one before the endpoint, with a LPS to avoid it from spreading electrical noise in the clean zone that was created.