I try to use Mic input.  The volume is very low.

Is there any setting to adjust the volume?

The reason is because Mic in and Aux in(Line in) use different volume.

Mic in：-70db~-40db

Aux in(line in)：-40db~0db

The jack could be used to connect Aux in and Mic in audio.  

To set it , you could use the Mic in gain option in iPad OnAir app.  The maximum is to gain 30db.