Apple tells you that you can now record multiple tracks at once. You plug your guitars in and nothing happens. Here’s what you need to do to get the band back together.
You’re going to create an Aggregate Device. This will alow you to have multiple devices plugged in to your Mac and have GarageBand recognize them individually instead of just one input.
Head on over to Utilities/Audio MIDI Setup. Navigate to the Menu Bar Window>Audio Devices.
Plug in all your fancy musical instruments.
Click on the + symbol in the Audio Devices window. Clcik on Aggregate Devices on your new item and give a name. We chose Geetars for our bass and electric guitars.
Your instruments and how they are connected to your Mac should show up on the right hand side of the Audio Devices window. Check the Use box next to the connections of your instruments. We utilized the Built-in Input for the guitar and an XLR to USB converter called the CEntrance MicPort Pro for our bass.
Launch GarageBand and head on over to GarageBand>Preferences. Click on the Audio/MIDI tab and select your new Audio Input device.
Head up to the Menu Bar and select Track > Enable Multitrack Recording.
In your project, create Real Instrument tracks for your instruments. Don’t bother with Electric Guitar track, it won’t work.
Select each track and click on the i in the lower right hand corner. From there you can select the Input Source for each track.
You can connect up to eight instruments like this. That’s half of the Arcade Fire connected to one Mac.