iOS line in via headphone jack (adapter?)

Question

I want to record an audio signal with my Audio Unit on my iPhone which comes from a normal 3.5mm audio cable (e.g. with another iPhone acting as sound source).

A direct line-in is not possible, because the iPhone has a 4 port headphone jack. I tried different kinds of these adapters: http://www.amazon.com/StarTech-com-headsets-separate-headphone-microphone/dp/B004SP0WAQ/ref=sr_1_3?ie=UTF8&qid=1446196112&sr=8-3&keywords=3.5mm+headphone+mic+splitter

But none of these worked.

Am I doing something wrong? What else could I try?

Thanks a lot and have a nice day!

Answer 1

You have to match the expected impedance for the microphone. Otherwise the device treats it as if it weren't there. Check this out for details.