Creating sound in APP

Hey guys,

I am creating an appInventor app that uses audio (voice no music). I have created the audio in .wav format which sounds just ok but the app is 13mb too large to package as an .apk.

When I compress the sound files to mp3, they are really unprofessional and have a metallic mono sound to it.

I have used several software to try and clean it up and make the volume higher but I am at a loss.

My question(s) to you:

Is there anything else I could try to make the sound better? (software, perhaps)

Is the quality from mp3 the best I can expect?

Is there a typical or standard set of settings I should use when recording voice?

This is the final stage of my APP and is the only thing that might prevent it from going from 4 to a 5 star rating.

Thank you all in advance.