In a recent update, Apple made the iOS version of GarageBand compatible with the popular audio-channeling utility Audiobus. Although Apple provides ways for some apps to communicate with others--Facebook and Twitter hooks built into iOS, for example--until Audiobus came along, moving sound between iOS music apps was a clumsy process that required saving and exporting audio files and then importing them into compatible apps.
What Audiobus brings to the table is the ability for compatible apps to communicate with one another, much as PC and Mac audio applications have been able to do for years. In this case you can designate up to three apps as an audio source--two synthesizer apps and a drum machine, for example--plus another that can apply effects to the sound emanating from the source app, and an output app that is most often used for recording the combined results of the input and effects apps. With this update, GarageBand becomes a compatible output destination.
The Audiobus workflow
To begin, you need at least one compatible input app and a copy of GarageBand for iOS. Audiobus has a webpage that lists compatible apps; or you can launch the Audiobus app, tap the Apps button at the bottom of the screen, and see the same list, complete with links to the iTunes Store.
Stacking inputs in Audiobus
Launch Audiobus, and you see a simple interface that includes three boxes--Input, Effects, and Output--each bearing a Plus (+) icon. Tap the Input box, and a list of compatible apps on your iOS device appears. Tap one you wish to use, and the box expands--showing a gray box that you tap to launch that app, as well as another box that holds a Plus icon for adding another app. Once the app launches, you should be switched back to Audiobus.
To use the selected app, tap its icon in Audiobus; you'll then switch to that app, and a small palette will appear along the right side of the app's screen. It's from this palette that you can return to Audiobus by tapping a Return icon or move to another app using Audiobus by tapping its icon and then the Return button associated with that app.
As mentioned, you can specify up to two additional input apps. You might do this, for example, if you wish to layer multiple apps as a single input source. Or, if one app is a drum sequencer or an app that includes an arpeggiator, you could have that playing in the background while you jam on a different app. To remove an app, simply tap on the Eject button below or to the side of it.
The Effects box is next in the signal path and uses the assigned app to alter the sound coming from the input app(s). Unlike the input source, you can have just a single effects app, and you can switch that effect on or off from within the Audiobus palette (as well as move to the effect app by tapping its Return button in the palette).
GarageBand as output destination
The Output box is where GarageBand comes in. To use GarageBand with Audiobus you first launch GarageBand and set up a song. Just as with any other new GarageBand project, you must define the length of sections. For example, if you want to record more than 8 measures you must tap GarageBand's Plus (+) button, found near the top-right corner of the display, and choose the number of bars your section will have. Also, you may wish to hear a four-beat count-off, but not have the metronome clicking as you play. In that case, tap GarageBand's Settings button and configure the metronome appropriately.
Most important, you must choose an instrument type that's compatible with Audiobus. This includes the Guitar Amp, Audio Recorder, and Sampler instruments. The other instrument tracks use GarageBand's sampled instruments as an audio source, so they won't take input from Audiobus.
Which you choose ultimately depends on what you want to do with the recorded track. If you choose Guitar Amp, you have the option to apply GarageBand's amps and stompbox effects to it. Select Sampler, and you can then play and transpose the recorded track using the instrument's keyboard. And if you want a simple, "straight" recording, Audio Recorder is the way to go.
To record into GarageBand, switch to the input app you intend to play. Then tap the GarageBand icon in the Audiobus palette and tap Record (marked Rec). The Rec icon will turn red, and you'll hear any tracks you've already recorded as well as the metronome count-in and click if you've configured them to play. Tap Rec again to stop recording. To review your work, tap the Rewind to Beginning button in the palette and then tap Play.
With your recording completed, tap the Tracks button at the top of the GarageBand window, and your recorded tracks appear as expected. Any track that includes just a single input app will display that app's icon along with its name in the Tracks window. If your input source uses multiple apps, an Audiobus icon and name are shown in the track. Each track is a digital audio (or real instrument) track and can be edited as those types of tracks normally are.
Audiobus was an important utility for musicians before Apple joined the party, but with GarageBand's flexibility and low price, it's even more valuable now. If you're an iOS musician, you owe it to yourself to throw Audiobus and GarageBand together.