GarageBand can only output audio to a single device. Click the Output Device pop-up menu, then choose the device your headphones are connected to.To set the inputs and outputs for your recording, choose GarageBand > Settings (or Preferences) > Audio/MIDI, then do the following:.You can record multiple tracks at once with an Aggregate device in GarageBand, such as a podcast with multiple USB mics:

For each device that is not the clock source, select Drift Correction.

To set the clock source for the Aggregate Device, choose the device from the Clock Source menu. Choose the device with the most reliable clock.

Drag a device to the left for lower input or output numbers, or drag to the right for higher numbers.

To reorder devices after you've selected them, drag a device under Subdevices left or right.

Learn more about how to identify Aggregate Device inputs and outputs

With the new Aggregate Device selected in the sidebar, select the Use checkbox for each device you want to include as a subdevice in the Aggregate Device. The order in which you check the boxes determines the order of the inputs and outputs in applications like Logic Pro and MainStage.

A new Aggregate Device appears in the list on the left side of the window.

Click the Add (+) button at the bottom of the sidebar of the Audio Devices window, then chose Create Aggregate Device.

From the Finder, choose Go > Utilities, then open the Audio MIDI Setup application.And that’s it.When you create an Aggregate Device, make sure all external audio interfaces are connected to your Mac. If not, then plug the port adapter in too. Many USB audio devices are powered by the USB connection itself. USB hubs can cause complications, and even malfunctions. For best results, hook it direct to a USB port on your Mac. To get started with your USB audio interface, just plug it into a USB port. Plugging in and finding your new USB audio interface The familar volume menu item lets you select an output device for audio. In between there’s a huge range of options, from USB headphone amps costing many thousands of dollars, and meant for just one pair of headphones, to budget mixers that let musicians record great quality audio at home on modest budgets. At the other end of the list is something like a mixing console, which will have many inputs, allowing your to hook up, say, 16 different inputs and have them all piped into your GarageBand app. These are popular with podcasters, for example. The simplest USB audio device is a USB microphone, which can be plugged direct into your computer and used to record.

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