I read the manual, but it’s ambiguous how this works.
If I connect a line level output using an XLR connector into the XLR inputs of the UR824:
Will it automatically switch to the mic input circuit, or does it sense the input type and use the correct line level input circuit?
or to put it another way:
are Jacks exclusively for line level inputs and XLRs exclusively for mic level inputs on this unit?
XLR and jack are just two different ways to connect something.
XLR contains grounding and jack does not, so in theory XLR can get better S/N ratio’s.
XLR is also a much more solid construction concept and it has potentially a lock system build in, so it can be a good idea under harsh usage conditions
In souncards it can happen that under XLR they provide more software functions like fantom power, input level control, and input-level switches but in real life they do just the same thing. Transferring a signal from point A to point B.
From block diagram in manual: The XLR and line inputs are wired together immediately and follow the same signal path. The exception is channel 1 and 2, where a Hi-Z source can be connected to the line jack only.
From experience: Aside from the Hi-Z switch on channels 1 and 2, the pad button and gain knob on each channel is what’s adjusting the level and gain. There’s no separate circuit path for mic versus line. I’d definitely engage the pad when using line-level sources.