Audiobus: Use your music apps together.
What is Audiobus? — Audiobus is an award-winning music app for iPhone and iPad which lets you use your other music apps together. Chain effects on your favourite synth, run the output of apps or Audio Units into an app like GarageBand or Loopy, or select a different audio interface output for each app. Route MIDI between apps — drive a synth from a MIDI sequencer, or add an arpeggiator to your MIDI keyboard — or sync with your external MIDI gear. And control your entire setup from a MIDI controller.
Download on the App StoreAudiobus is the app that makes the rest of your setup better.
New Audio Mastering app
Just ran across this post on the developers website
http://audio-mastering-studio.blogspot.co.uk/2013/12/happy-new-year.html?m=1
Basically a new version reworked from the ground up. He says it will be among the best sounding master effects available on ios currently. Sounds pretty great overall. New sound engine and the quality of sound "Will be better than any thing else available on ios currently". Almost sounds too good to be true - but this developer seems to have a proven track record. Lets hope it's as good as it sounds.