Question

I am NOT using an  interface. The mike us plugged directly into the iMac. Garageband has no problems-

Why hasn't Personus answered this question yet?

Update Q on 10-01-2016: Is the use of an audio interface essential in order to get the usb mic to work?

Answer 1

The device must be selected as your Audio Device in the Preferences section of Studio One.

Keep in mind that you can only have one Audio Device at a time; if you select the USB mic as your Audio Device then you will not be able to hear anything until you switch back to your other sound driver. The ideal solution is to use an interface with a regular mic, and attach your speakers or headphones to the interface instead of your computer.

Answer 2

Using El Capitan, AT2020 and even tried an aggregate device.  ST1 does not show any signal.  GB does!  Arghhh!