Although in theory USB can be used for both audio and MIDI, very few keyboards support that (the only Roland with that feature is Fantom).
Fantom-06/07/08, FP-E50, RD-88, FP30/60/90X, ...
Basically all of the new(ish) Rolands carry audio and midi over USB. The older models, like the DS en FA series, for example, of course, don't...
It's just that I've been spending some time on the Roland site lately now that I've bought a FP-E50.
Sorry for the hijack !
Okay what if I have a newer iPhone. All I have is the lighting to usb camera adapter connected from the Juno to my phone. Do I need a different type of adapter?
I know there are Lightning splitters (1 lightning to 2 lightning ports, 1 lightning to 1 USB and audio mini-jack out ) from various brands but no idea if they work well.
Basically, you'd need something like the Apple camera adapter but with an extra 3.5 audio out port. Don't know if that exists but maybe it's possible to combine several cables/adapters, don't know.
Or perhaps a Bluetooth dongle ? Just plug it into your DS and pair it with the iPhone ? If it's just to play along, there wouldn't be any delay issues.
Something like this :
Tone:Link - Blackstar (blackstaramps.com)