This has been a problem (for me) for years. Basically, your expression pedal with the 1/4" input is a MIDI thing; that 1/4" connector expects to plug in to another MIDI controller (like a keyboard) as part of an overall MIDI control system. So you can get something like the IKM Blueboard or another third-party guitar-FX MIDI controller with either Bluetooth or USB (and run your expression pedal into the controller, and then the controller into your computer),
or you can try to get a standalone MIDI-to-USB adapter (and plug your expression pedal into that, and then it into your computer).
Where I am (S. America) such solutions are costly, and I've always judged the risk of it simply not working as expected (and/or the requirement to pay for hardware features I don't actually care about!) to have been too great to try anything along those lines.
I myself
just got a new 2i2 a few months ago, and I expect that to last me some years. If it had been available a few months ago, I might have gotten newly released iRig Stomp I/O instead: it has a built-in expression pedal
and an XLR/instrument input with phantom power (which, IMO, was the major piece of the puzzle missing from previous IKM guitar/audio interfaces). The only downside of the iRig Stomp I/O that I see is that there is just a
single XLR/instrument input, so I can have either the mic or and instrument plugged in, but I can't just leave both plugged in and ready to go, as I currently do with the 2i2. Still, perhaps in some years, by the time I'm needing to replace the 2i2, there will be an "iRig Stomp I/O 2" or "HD" with two audio inputs. (Basically, I want a 2i2 with an expression pedal!
)
