I wish I had known this years ago when I ran the Media Cloisters! It turns out you can connect multiple USB inputs and outputs on Macs. This is great if you want to team-edit video or record two people at once. You’ll need two USB headsets for this to work.
Getting Two USB Headsets to Work:
This is built-in functionality for Mac OSX. Plug in both headphones, then open Audio Midi setup from /Applications/Utilities.
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Find the Audio Midi Setup by searching “midi” in the spotlight
Click the plus in the lower left corner and choose “Create Multi-Output Device.”
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Make two usb headsets play together!
Check the checkboxes beside both headphones.
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Uncheck the built-in output.
If you want to rename your new virtual device, you can double click the new entry in the list on the left and give it a name like “Both headphones.”
In System Preferences, you can now set the output to go to your new Multi-Output Device.
Setting up Two USB Headphones Mics
A similar arrangement will work to create two USB inputs. Create an aggregate device for the USB headsets.
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Make two mics record on separate channels!
Check the appropriate boxes.
To record in Audacity onto two separate channels, choose “(Stereo) Recording Channels” as your input: