Today I learned something about my Focusrite Scarlett 18i20 that I somehow completely overlooked: the line outputs are balanced TRS outputs.
Which also means: if you’re running those outputs to DIs, you should be using balanced TRS cables. Or, depending on the setup, you can use balanced TRS-to-XLR cables and go straight into the mixing desk.
I had been using unbalanced TS jack cables. That works, but it also makes the connection much more susceptible to electrical interference, ground-related noise, etc. In my case this resulted in a low but clearly audible noise in the signal.
The funny thing is that I only really started noticing it because our live setup has gradually improved. Better equipment, better monitoring, better IEM sound… and suddenly little problems that probably had been there for a while became much more obvious.
Naturally, my first suspect was Gig Performer 
I went through my GP project looking for anything that could be generating noise: plugins with some kind of analog/noise modelling enabled, gain staging issues, something weird in the audio chain, etc. But everything inside GP was clean.
Eventually I traced it back to the cabling after the interface.
Swapping the unbalanced TS connections for balanced ones made the difference.
Probably very basic knowledge for a lot of people here, but I thought I’d share it because it’s an easy thing to overlook when building a live rig piece by piece. And if you’re hearing unexplained noise from your GP rig, it might be worth checking not only what happens inside Gig Performer, but also how your interface outputs are connected to the rest of the system.
