How do I change the microphone input sensitivity on iPad 2? Is it possible to change the microphone sensitivity (input volume) on the iPad?

If so, how?
What you can do with the built-in microphone is limited. You should investigate purchasing a third-party microphone, or better yet an audio interface with a microphone preamplifier, into which you plug a microphone. This will cost money but give you much more control.

Look for products from Tascam, Apogee, Line 6, IK Multimedia, and Griffin.