Noel reviewed SoundCell and SoundPrism on the iPad.
SoundCell is more of an app to make rhythms and goof around with music. It costs $1- it's worth it to buy but not necessarily educational.
SoundPrism can be used to record as well as to change/modify sounds and hear specific notes, so it can be used for education purposes. Plus it's FREE, so that's an added bonus. If you want to change the sound on this app, you can use multiple fingers instead of just playing 1 note. Noel would recommend this app for an advanced level music class.