Scarlett Solo with Headphones in Output and Mic in Input: mic sound works in Discord but not in OBS

[Zakch93]

I literally just tested it to be sure. I switched Monitoring to my other earbuds connected via 3.5mm to the PC and I can hear the mic in OBS, but I can't hear it with the Headphones in the Scarlett and it doesn't even get recorded in OBS. Please help.

 

[Zakch93]

OK so changing headphones from right to left output on the Solo fixes it, but I'd like to get an explanation as to why.