How to connect an external microphone/synthesizer/guitar to the Android/iOS device?
Русская версия здесь

There are several ways to do it.
  • Use Line 6 Mobile In (only for iOS).
  • Use some external USB audio interface.
  • Use headphone jack of your device (only 3.5mm TRRS compatible) with adapter (for instance, iRig, kVconnection, Headset Splitter Adapter etc).
  • Build your own adapter for headphone jack (only 3.5mm TRRS compatible). The circuit diagram is below. Note that the GND and the MIC pins may be swapped on some non-iOS devices with OMTP standard!