Introduced with iOS 7 and available on all iOS devices, Apple’s inter-app audio feature allows compatible apps to share audio streams and MIDI with each other, making it possible to work with multiple apps in a relatively seamless manner. Let’s take a look at how to use it.
In Inter-App audio, there are two types of apps: Nodes, are Instrument and effect apps whose outputs are made available to other apps. A Host is an app (usually a recorder or DAW) whose input is made available to the Nodes.
Non standard
One of the confusing aspects of Inter-App audio, as opposed to Audiobus, which is a third-party option for audio integration among apps, is that every app implements it a little differently, which can sometimes be confusing. For example, Inter-App audio transport controls appear on all Node apps, and are typically right on the main screen, but on Arturia’s iMini app (a superb Minimoog emulation), I couldn’t find them until I tapped a disclosure arrow entitled Connect, which revealed them.
For instance
Here’s a step-by-step look at at configuring an Inter-App Audio setup, using Apple GarageBand (free in iOS 7) as a host, and Tempo Rubato’s NLog Synth Pro as an instrument Node.
 1. After launching GarageBand, I’ll open the My Songs window. From there I can create a new project or open an existing one. I’ll choose to create one. |
 2. This takes me to a window where I choose a track type for my first track, and I’ll slide until I get to Inter-App Audio, and then tap it. |
 3. That brings up a screen showing compatible Inter-App Audio Nodes. The tab at the top lets me look at either instruments or effects. I’ll tap the icon for Tempo Rubato’s NLog Synth Pro app. |
 4. Pressing that opens NLog Synth Pro featuring Inter-App Audio controls above the keys. I can put GarageBand into record right from here and start playing the synth. |
 If the Metronome and Count-off features of GarageBand have been activated, I’ll get a count off first and a click for reference as I record. |
 If my project has existing tracks in it, I’ll be able to hear them as I record my track from NLog Synth Pro. |
 5. Tapping the GarageBand icon in the Inter-App Audio transport controls in NLog Synth Pro takes me to GarageBand’s audio recorder window. There, I see the Inter-App Audio jack icon along with the NLog Synth Pro icon. |
 6. Tapping the jack icon opens the Input Settings dialog, from where I can open the Inter-App Audio dialog (shown). From there I can add an effect to process the synth on its way into GarageBand. |
MIDI, too
Inter-App Audio can be implemented in compatible MIDI apps, too. For example, the MIDI workstation app Tabletop includes an Inter-App Audio MIDI controller called Mastermind as one of the modular instruments that you can use within it. After you’ve added it to a setup, and opened it, you can choose an Inter-App Audio instrument in its Select App window, which can then be played from the onscreen keyboard, and its audio will be routed to Tabletop’s mixer.
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A simple setup in Tabletop with Mastermind added |
 Mastermind’s Select App window lets you choose a MIDI instrument to control |
More to come
As you can see from those examples, Inter-App Audio is a powerful feature in Apple’s iOS, and once even more apps become compatible, it will be even more so.