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.
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