Having the equivalent of a recording studio in your pocket is a boon for audio geeks. FourTrack records, mixes and plays (as implied) up to four tracks. Throw in the ability to set playback levels, skip through tracks, pan audio, support multiple formats, import audio from an email attachment, sync with your computer via Wi-Fi and intuitively control all the action with clever controls and you're on to a winner.
Music Theory for Beginners, £2.99
This app promises to make music maths fun – it certainly beats listening to your music teacher droning on about harmonic intervals and church modes. Constructed and tested by a bunch of accomplished musicians and theorists, you can download safe in the knowledge that what's being spouted at you is reliable. Although you may get annoyed by the owl (you'll see).
Korg iElectribe Gorillaz edition, £13.99
The Gorillaz created an entire album with iPad software, don't you know, and KORG's iElectribe app was one of their main musical tools. This Gorilaz-tuned edition features 128 sounds and 64 preset patterns taken from the album, The Fall. And if you think you can do a better job, you can have a bash at remixing parts of their album.
Yamaha TNR-i, £13.99
Its interface might look like a complex version of Simon, but the TNR-i app's 16 x 16 grid of buttons equips you with the ability to create your own masterpiece using synthesized beats, loops, recurring patterns and rhythms. Obviously it's not as fully featured as the original Yamaha Tenori-On, but you're saving £390.
If you're after a proper DJ app, look no further. Transform your iPad or iPhone into a proper pair of mixing decks. Load up choons from your iTunes library, then attempt your best Westwood impression by beat syncing, scratching and transitioning between songs like a pro. You can even hit the record button and play your mixes back to whoever will listen. Pair it with Numark's iDJ Live and you'll be a superstar Djay before you can say, "There's an app for that."