Audiobus is a £6 third-party utility (currently on sale for £2.99) for iOS that lets users pipe audio between apps. That way you can, for example, combine audio from a drum machine app with audio from a synthesizer app. Among the apps that already support Audiobus are Animoog, ThumbJam, Samplr, DM1 - The Drum Machine, and all of Korg's apps. And now, GarageBand joins that list.
With the latest version of GarageBand, Audiobus users can now play and record music from compatible apps within Apple's recording software. Apple says that the £2.99 GarageBand is the App Store's most popular music creation app.
The Audiobus integration follows a consistent path that Apple has been taking. The company has incorporated popular and emerging third-party technology into its apps for a while now--including Facebook, Twitter, and Sound Cloud--and the Audiobus compatibility for GarageBand continues that trend in a new way: direct interactions with a third-party app.
Audiobus requires an iPhone 4S or newer, a fourth-generation iPod touch or newer, or an iPad 2 or newer.
Also new in version 1.4 of GarageBand for iOS is the option to disable snap-to-grid when editing, and a fix for an issue with feedback.