Turn Your iPad into a Music Synth Workstation

Link your iOS music apps together with Audiobus
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Audiobus can route audio signals between compatible apps in much the same way as a computer-based DAW. More than 200 iOS apps currently support Audiobus, and hundreds more are on the way.

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IF YOU use an iPad or iPhone to make music, you’ve probably heard of Audiobus, and you may be using it already. Audiobus is an iOS app from an Australian company called A Tasty Pixel. It routes audio between other apps, which makes recording software instruments on your handheld device more like recording plug-ins on your computer. You can stream audio from a synth app, for example, process it with an effects app, and then capture the results into a multitrack recording app— something that was previously impossible in real time on the iOS platform.

Audiobus’s Connections page presents you with three audio-routing stages: Input, Effects, and Output. Touching the Input button will list all your Audiobus-compatible apps that produce sound. When you select one from the list to load it, the onscreen graphics will indicate that it’s asleep until you launch the app by touching the Input button a second time. Likewise, the Effects button lets you access apps that can process audio signals, and the Output button lets you specify their destination from a list of Audiobus-compatible apps.

Once your apps are loaded, a dock called the Connection Panel will appear on the side or bottom of each app’s screen, allowing you to easily switch to other apps and access remote-control buttons. Exactly what those buttons do will depend on the app type. Usually, drum machines and sequencers provide buttons to turn playback on and off; recorders provide buttons to start and stop recording and playback; and effects provide buttons to toggle bypass.

Drive the Bus to the Garage Perhaps the biggest news for Audiobus came when Apple added Audiobus support in GarageBand for iOS. GarageBand is by far the most popular multi-track recording app in iOS, so let’s take a quick look at using GarageBand with Audiobus.

Open Audiobus, select your favorite Audiobus-compatible synth app as the input, and select GarageBand as the output. Open GarageBand, add a track, and assign it to Audio Recorder. Switch to your synth app, touch GarageBand’s Record button in the Connection Panel, wait for the count-in, and begin recording. Touch Record again to stop and Play to hear what you’ve recorded.

Now switch back to Audiobus and select another instrument app as the input. Switch to GarageBand again and add a second audio track. Switch to the second instrument, touch Record, and lay down your second track. Repeat this procedure until you’re happy with the results. Notice that every time you add a new audio track, it will record whichever instrument app is onscreen when you touch Record in the Connection Panel.

Uptight, out of Sync This process isn’t without problems. Because Audiobus handles audio only and not MIDI clock, as of this writing, it can’t sync tempos between GarageBand and other apps. If you’re recording a drum machine app or a synth’s onboard sequencer, then you should try to match tempos manually to get an accurate count-in when you record, and then leave GarageBand’s metronome turned off.

The good news is that an app called Jack from Crudebyte combines audio and MIDI routing, making synchronization possible. The bad news is that less than one-tenth as many apps support Jack as support Audiobus, and GarageBand isn’t one of them. Fortunately, A Tasty Pixel is working to expand Audiobus’s capabilities to encompass tempo sync, which will put the iPad and iPhone a few steps closer to being versatile and truly portable synth workstations.

Geary Yelton is former senior editor at Electronic Musician. He lives in Asheville, North Carolina, and takes his iPad everywhere.