OS X has a neat feature you might not know about: it can create an aggregate set of audio devices so you can use multiple inputs and outputs in any application, allowing you to configure custom surround sound setups, record from more than one audio interface at a time, and more.


If you've been working with audio in OS X for awhile you may remember that you could only use one CoreAudio input/output device at a time. That meant your internal sound card, an external USB audio interface, or the microphone on your webcam—but not all of them. That changed somewhat recently, although I'm not sure how far back. The point is, if you haven't explored aggregate audio settings you should to see if there's anything it can do for you.

Setting up your own aggregate audio device is really simple. Just follow these steps:


Open up Audio MIDI Setup (in Your Hard Drive -> Applications -> Utilities).

Click the + button in the bottom left-hand corner and choose "Create Aggregate Device."

Double click on the name "Aggregate Device" to rename it (if you want to).

In the panel on the right side-side, choose any input and output devices you want to be able to access through this aggregate device. Once you've made your selections, you're done!

So what can you do with your aggregate device? If you have multiple audio outputs, you can use multiple sets of speakers to either pump audio into a different room or create a surround-sound setup. If you want to record from microphones and a Skype call for a podcast, you can download Soundflower to record computer audio and create an aggregate device with it and the audio interface responsible for your microphone(s). If you want to record multiple microphones but can only hook up a maximum of two (for example) to each audio interface, just aggregate your audio interfaces and record from all your microphones at once.

If you're working with audio on a Mac, there are a lot of ways this can be useful. These are just a few examples. I hadn't bothered with this feature until I was looking for an easier way to integrate audio from Skype guests into our podcasts. Learning how it worked helped me solve that problem easily. It's just one of those hidden features worth knowing about.