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.
Comments
It's difficult to give a good answer without knowing what tools you have available. How did you record the loop in the first place?
GarageBand is free, and would also be an excellent way to do this. You just need to learn how to handle audio files in it. GarageBand is one of the easiest to use DAWs and is great for those just learning their way around music production.
You can also do it audio editor such as Neon Audio Editor.
[Edit: Note to self. Check the forum section before responding. Sorry, I now see the question was about Loopy Pro.]
You could overdub onto it if the length is right. You could also set the loop to play once and resample into a new loop whose length can be whatever you want it to be.
That's what I was wondering. But then I thought maybe the loop needs to be a specify length/duration. Hence the question.
If you swipe up on the loop, and then tap extend, it will double the length of the loop, adding silence at the end. You can then use overdub to record into that new region