How do I use multiple USB Microphones in Garageband?

For this answer, I'm going to use two microphones. One is a Logitech G330, and the other a Griffin iMic. I'll combine these two devices into a single Aggregate Device which will allow me to use each mic as a channel in Garageband. I'm using Garageband version 5.1, and Audio MIDI Setup version 3.01. If you're using different versions, your screens make look and act slightly different.

To start, unplug your microphones so you can follow along. Open Audio MIDI Setup from within your Utilities Folder. The Utilities folders is in your Applications folder (in case you're wondering).

Make sure you're in the Audio Devices window by choosing Show Audio Devices from the Window menu. If you're in the right place, you'll see a screen that looks something like the picture below.

Plug in your microphones. As you plug in your microphones, you'll see them appear on the left side of the window.

Next you'll create the Aggregate Device. Click the Add Device (the +) at the bottom left of the window.

A new device will appear named "Aggregate Device."

If you're going to using several configurations, it helps to give each configuration (Aggregate Device) a unique name. I chose "Multiple Mics" for this tutorial.

Make sure you've clicked the new Aggregate Device, and you'll see a list of audio devices on the right. This list only includes real audio devices, and won't include other aggregate devices you may add.

The next step is to choose which audio devices you want to include in your new Aggregate Device. I chose the "Logitech G330 Headset," and the "iMic USB audio adaptor." The iMic has an input and an output (you'll see each listed). Notice that each iMic has their function listed in the "In" and "Out" columns.

Sometimes you may need to adjust the "Clock Source:" and the "Resample" options. Click the purple question mark to activate Apple's Help System if you need more on how those work. A tell tale sign that you'll need to adjust these settings is that one of your microphones will sound fuzzy or "digital."

Great work! Now you have what appears to be a new microphone to all of the programs on your Mac.

Now let's open Garageband, and choose Podcast as our new project!

The default setting for a new Podcast in Garageband will have two audio tracks. Click the first track, which is named "Male Voice." That sets this track as active, and allows us to change setting for just this track. Notice the I in the bottom right corner of the window. This allows us to set the microphone settings and voice effects. Go ahead and click the I now.

Have a look at the Input Source menu. You'll notice that there are several sources listed, all created by our Aggregate Device settings. The names all reflect the name we gave the Aggregate Device (in my case, "Multiple Mics." You can choose to use your mic's a stereo, or mono depending on your needs. Since the "virtual" devices aren't named, you can just look at your Audio MIDI Setup window to see which order they appear in.

In my case, I wanted to assign the Logitech G330 to the "Male Voice" track.

The other track is set to use the Griffin iMic microphone.

A closing thought: if you want to record from both of these devices simultaneously, be sure to click the record button for both tracks.

There you have it. Two microphones in Garageband, with no additional software or hardware. You can use as many microphones this way as you have USB ports.