I’ve done this quite a lot - in different setup iterations… now it’s a lot more straight-forward if you’re using the Digi machines (in my case, my set revolves mostly around the Digitakt) since you can do class compliant audio+MIDI over USB.
Although I eventually settled on Digitakt+Octatrack (more on this later), I’ve been doing some new tests using Digitakt +iPad + Faderfox UC4 (for a super portable, powerful setup).
I use AUM (essential imho) as a mixer, and Enso as an AUv3 looper. The most complicated part is the crossfading. If you use two faders, you’re all good - but if you’re a nerd like me and want to crossfade with a single fader, same as a dj mixer, it’s a bit more complicated.
Yes, you can map a single fader with opposite values as to raise the volume on one track while lowering the other… but in that case, both tracks end up having 50% gain in the middle - which is not how crossfaders work. To address this, I bought another app called MIDIFlow (can’t remember if it’s free, but I know that I bought and Inter-App Purchase module to be able to do this) and configured in such a way as to have logarithmic curves for the faders… it’s too boring and long to explain here, but just to note it takes a bit of planning, if you want to do it this way.
I’ve also used Kaoss Pad 3 to transition in the past (the only gear I bought - and sold - twice)… while it’s absolutely great for looping and sync is pretty great for transitioning between patterns, the effect quality is not great (more quantity than quality) and it ended being a bit complicated for whole other aspects. First of all, I needed a dj mixer or something to crossfade between the OG signal and the loop - and also, if I wanted to use KP3’s effects on the loop, I would have to remember to change the input to the mic (as to avoid the OG signal to come through as well as the loop when pressing on the XY pad)… and of course this would mean remembering to switch it back to the RCA input before looping the next pattern.
I finally went back to using my Octatrack for live performance, since it seemed more stable/easier for me (as a mixer, stem/long audio player, transitioning between tracks, fx box, etc.)
I did look into the 1010BB (portable, dead simple to use, multiple outputs, good for sketching ideas and recording long stems) but I decided I have more than enough gear already, plus I feel I might be able to pull something better for my workflow using Digitakt + iPad, an enviroment I already own and know.
As a sidenote, I can’t believe there isn’t any (single-device) alternative other than the Octatrack for transitioning from source to loop with a crossfader. Seems like a pretty big gap in the hardware musician world, and that it could be solved with a well-thought out, portable option.
Anyway, sorry for the long post!