Please see Installation: Do NOT run Audacity from the DMG!!! . Make sure you get Audacity 2.0.5 from Audacity ® | Download for Mac OS .
Why are you generating a tone?
If you have a USB cassette player, try following our Manual: Audacity Manual . Get the USB device recognised by Mac so that you can see it in System Preferences > Sound. Play a tape and make sure the blue “Input level” meter in “Sound” bounces left and right.
Then if Audacity is already running, either restart it or use Transport > Rescan Audio Devices from the top of the Audacity window. Audacity can’t see a USB device if you plug it in after launching Audacity.
Please give the make and model number of the USB player (or whatever it is) if you need help.
Gale