Tutorial: Combining Audio Devices in Macs

This is going to be for the Mac users, so if you are a PC user, sorry.  This functionality is exclusive to Macs (as far as I know, but I will investigate).

Lets say you started out your podcasting career needing only one or two inputs.  You were podcasting by yourself or a friend, or just needed enough inputs to for you to talk to someone on Skype.  Now you have grown a bit, or have a sudden need for more inputs, and you don’t want to just give up on your old device.

Mac OS X has a nifty setting that lets you combine multiple audio devices into one virtual audio device.  You tell your computer which audio devices you want to combine, and it makes a new single source that your computer sees, will all the inputs and outputs of both.

On this computer, I’m running OS X 10.6.8 as it’s a four year old computer and it works well for what I do.  In the newer versions of OS X, the steps are the same.

First, I have two devices connected to my computer.  One is a Firewire mixer and one is a USB interface, but the connections themselves don’t matter.  This is something you could do with several USB Microphones, or any combination of devices.

Mackie Onyx 1220i and Alesis io2

Mackie Onyx 1220i and Alesis io2

Next we need to open the Audio Midi Setup utility.  You can find it in your Applications folder under Utilities > Audio Midi Setup.  It is not the same as the Sound settings under System Preferences.

Audio MIDI Setup Initial Screen Cap

When you open Audio Midi Setup, you should see all your audio devices.  If you don’t, go to your toolbar and click Window > Show Audio Window.  You can see the two devices I’m going to combine, the Mackie Onyx mixer, and the Alesis io2.

Next, click the plus button in the lower left of the window.  You’ve just created an aggregate device.

Audio MIDI Setup Device Made

On the right of the window is all the devices you can add.  You may notice that every devices listed on the left isn’t available.  Some of those devices on the left are virtual devices that aren’t available because the software that uses them isn’t running.  But Soundflower, a virtual audio device is available.

I’m just going to select the two devices I want to combine.  I could add more if I needed them, but I’m keeping it simple.

Audio MIDI Setup Selected

The aggregate device settings is going to ask you to select the Clock Source.  One of your devices has to act as a master clock to keep all the devices synced up.  I selected the Mackie mixer to be the clock, and the io2 will follow that.  The ‘resample’ box is checked, because the syncing of the two devices is happening inside the computer, rather than via external means, such as a word clock sync (if you don’t know what that means, don’t worry, it’s mostly stuff that happens in recording studios and higher level recording setups).

If you click on the individual devices within the aggregate device, you can set the sample rate and bit depth, as well as other options.

Audio MIDI Setup Selection

Make sure the settings of the two devices match.  The Mackie has more available sample rates than the Alesis, so I select it’s sample rate and bit depth first, then make the Alesis match that.

So now I have  a single 18 input, 4 output device for my DAW to use. Double clicking on the name of the device will allow you to rename it to something easier to remember.  I named mine Mackie and Alesis.

And now I can select it from my list of devices.

Logic Pro Select Device

A few things to keep in mind about aggregate devices:

– Since these devices are combined in the computer, all of the audio has to be processed by your computer.  You can’t hear an audio input from one device on the other without latency or having to mix the sources in software.

– You can’t force a sample rate and bit depth on a device that the hardware isn’t capable of.  The Mackie mixer may be able to use am 88,200 Hz sample rate, but the Alesis simple can’t, and just because I combined the two devices, I can’t force it to.

Depending on your needs, it may make more sense for you to buy a larger capacity audio interface rather than use an aggregate device, but if you decide you just need to add something else to your existing rig, aggregate devices make it simple.


Have you used aggregate devices?  Have tips about using them?  Questions about what is posted here, or is there something I missed ?  The comments are open.




  1. Steve Bosman says:

    Thanks for your tutorial. I found it though an online forum u posted on. However, I still have the same problem as the original poster. I have 2 Yeti Blue USB mics and after trying on multiple macs I can not get the mac to see both of them at the same time. It will only ever show the last one connected. Any help you can give will be apprecated.

    • Hi Steve – The first thing I would try is doing the same thing with two different devices. Do you have another USB interface lying around? Can you borrow one from a friend? My thought is that as you connect two of the same unit, your computer doesn’t know how to separate them.

      Also, are you using a USB hub or going into two USB posts directly on your computer? If a hub, is it a powered hub?

      Mind you, I believe I have seen Yeti mics combined in the past. So this should be doable.

      Blue also has a service area, and you can find it here.

      Let me know what you find out. If I had the hardware you have, I would start testing it myself. I’m sorry I can’t help too much with this, but will keep my eyes peeled for anything helpful.

  2. David Boroditsky says:

    I’m having exactly the same issue: 2 yeti microphones, the mac only sees the last one connected. Was there ever a solution found?

  3. Hi, the whole thing is going well here and ofcourse every one is
    sharing facts, that’s genuinely fine, keep up writing.

  4. Most Blue microphones ship from the factory with identical serial numbers (I guess that makes them the opposite of serial… ) so the Mac sees them as the same device. You can verify this by looking in System Report (Apple logo -> About This Mac -> System Report) and clicking on USB. If you ship it in to the factory, they will flash the USB and give it a unique identifier in the serial number.


  1. […] into one virtual device called an Aggregate Device. I wrote a little tutorial on how to do it here. I don’t know of any way to do this on a […]

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