I am trying to use the Audio MIDI Setup program to aggregate two USB Sennheiser PC8 stereo headsets so I can use both simultaneously on Skype calls and GarageBand recordings. So far I am only able to use one at a time by deselecting the other USB device under the newly created aggregate device. How can I get both two work at the same time!?


Screen Grab of Audio MIDI Setup

  • Purchased a different headset to see if it was just a case of OS X being unable to distinguish between two USB devices with exactly the same ID... not the case. Although now Audio MIDI Setup now assigns different channels to each USB device, they still don't work in aggregate in any applications.
    – derek
    Feb 24, 2015 at 1:33

1 Answer 1


Not sure it's going to work using an Aggregate Device - each output must have its own channel that way.

Look at a Multi-Output Device instead - then channels can share one output.

You of course, don't need to use the same 'device' for both input & output, so you can set up a different one for input - though I'm still not certain you will be able to listen to [record] both mics at the same time, the same considerations may apply.

I can't test on USB headphones as I don't have any, but using this setup I can play iTunes over internal speakers and my dedicated sound card at the same time
sounds horrible, of course;)

enter image description here

  • Thank you for the reply and for trying this on your own! I'm actually experiencing the same issue with just the USB headset and the built-in speakers. In trying to create an aggregate device containing both of them, the output channels are both set to "2", and so I am only able to hear audio out of one at a time (similar to what I highlighted in the screenshot above). However, using the multi-output conf. I can get audio out of both devices simultaneously, so that does fix things! Unfortunately, what I'm really trying to do here is combine both mic inputs, and multi-out doesn't fix that!
    – derek
    Feb 23, 2015 at 19:31
  • You might possibly be able to make some headway with Soundflower or maybe LineIn, both from Rogue Amoeba - but I've never tried 2 inputs at once. [nor 2 o/ps at once til today;) I think you might be hitting hardware/driver limitations. Even ASIO only does one at a time, even though you can sub-mix to your heart's content within the environment.
    – Tetsujin
    Feb 23, 2015 at 19:35
  • Haha yes this is certainly uncharted territory for me as well!
    – derek
    Feb 23, 2015 at 19:47
  • Downloading Soundflower now... looks really cool! Thanks for the suggestion. To expand on my previous comments and yours about hw limitations, trying the same sort of aggregation with the built-in mic and USB mic from the headset yields the same results as trying to use two headsets... frustrating! If Soundflower is unable to help me rectify the problem I may just have to give up and get a mixer...
    – derek
    Feb 23, 2015 at 19:50
  • My understanding is that the aggregate device will enable you to "build" a 2-input device from two USB devices, recordable as 2 tracks in Garageband (i.e. it wont Mix them together), Whether this works for your hardware depends on an identifier- users reported sending their Blue Yetis back to be reprogrammed with a different ID so they could use two at once, but I don't know if this is also an issue for the Sennheisers? I have read that Audio Hijack can record two Yetis without reprogramming, so is not subject to the same limitation, but I haven't seen that confirmed. Mar 1, 2018 at 10:28

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .