Audiobus is an iOS app that allows other apps to work together as an audio-processing toolchain: play your MIDI keyboard into one app, run it through filters in other apps, and mix it in a third. All in real-time, foreground or background. That such a thing is possible on the locked down iOS platform is remarkable enough, but what's even more remarkable is that hundreds of audio apps have added Audiobus support in the few months since its debut, including Apple's own GarageBand. In this session, we'll take a look at the Audiobus SDK and see how to create inputs, outputs, and filters that can be managed by the Audiobus app to process audio in collaboration with other apps on the device.