Audio looping is so last season. MIDI looping is the future.
This app listens for MIDI note on/off commands and loops them with wanted looping period.
You can use either external MIDI sync or use app's own clock for tempo. It works with atleast Camera Kit and generic MIDI-USB-converter.
The app contains also a click sound that can be used to trigger other synths that have audio level sync-in. For example Teenage Engineering PO-12, PO-14 and PO-16.