thanks to everyone who replied, truly.
it seems that there are 2 solutions...
1) usb sound w/dedicated app
2) cable that turns L/R input from TRS tip to M input on TRRS tip
the 3.5mm/trrs/(left/right/ground/mic) socket on the phone should work as tdcrone
mentioned above. as long as a 3.5mm stereo+mic adapter available, or a custom cable that turns the original L or R input into M on the output end.
this is by far the simpler solution, **if such cable or adapter is available**, the caveat emptor is that the record will be mono
, and there could be mic gain issues
otoh, the usb solution works, at the cost of having to get an adapter and apps for android costs.
: i see that both USB audio recorder pro
and audio evolution mobile daw
seem to work with usb recorder, and the latter one is just marginally more expensive?
edit: sorry, just realise that one also needs to buy usb audio recorder pro if she/he wants to use audio evolution mobile daw to do usb record