GarageBand: Aggregate Device

Make sure Finder is active by clicking on its icon in the Dock

Open a new Finder Window


Select "Utilities" from the "Go" Menu


Find Audio MIDI Setup utility, and launch it

 

Once AMS is open, choose "open aggregate device Editor" from the audio menu.


And you'll see a window like this


Press the button, and a new aggregate device is created.

Double click the highlighted text, and enter a new name for your aggregate device. I'm going to name mine with the three devices I intend to use so that it will be easy to see of what this virtual device consists. This might be important if I were to create several different aggregate devices for different purposes at a future date.

Press return.

Now we can select the devices that we wish to add to our Aggregate Device.




Notice that the iMic is listed twice, First as an output device, and then as an input device. Since we're creating an input device, we're only interested in the latter.

One important note to mention is that all the devices have to have the same sample rate to work together. In the case of GarageBand that means a 44.1K sample rate (See: Setting Sample Rates and Bit Depth)

Click the button, and you can quit Audio MIDI Setup.

Now we are ready to make use of our new aggregate device in GarageBand. Open GarageBand's preferences.

Click the tab, and select your new aggregate device from the input popup menu



When GarageBand asks you...


Choose "Yes", wait a moment for the drivers to initialize, and now you can use any of the channels your Aggregate Devices consists of for multi-track recording.