See this page in the Audacity Manual: https://manual.audacityteam.org/man/error_opening_sound_device.html
WC
Do you have access to the unit and computer?
Close Audacity.
Plug in the Onyx and look for the USB light on the front.
I can’t tell if the Onyx has lights or some way to indicate volume. Does it? One of the interfaces by someone else has knobs that light up.
Connect the microphone and see if you can tell if there’s sound in the unit. Flashing lights, something.
As near as I can tell, there is no download instruction book for me to see.
Let us know. This is the troubleshooting technique where we start at the beginning and see where it fails. Please don’t leave out any steps.
Koz
Found it. There’s a tiny light by each volume control called SIG/OL. It turns green when the sound is normal and red when there is something wrong. Do you get any lights?
Koz
he used it to talk to me over skype.
It would be good to know that earlier. So the Mac thinks everything is OK.
Set the unit up normally and start or restart Audacity. Audacity checks for connections when it starts.
Audacity (desktop toolbar) > Preferences > Devices > Recording > Device. Does the Onyx show up there?
Does Mackie supply a software package or drivers?
Koz
Are they ASIO drivers? Audacity doesn’t easily support ASIO. I expect Audacity to recognize the Mackie and work with no drivers.
Koz
Audacity (desktop toolbar) > Preferences > Devices > Recording > Device. Does the Onyx show up there?
What does the Onyx setting say? Manufacturers have the option of custom labeling the connection or not. Did yours?
Koz