I am using a USB recorder box that has stereo inputs but only one gain control. When I use two microphone inputs how do I adjust each input?. I have no mixer facility but surely there is some adjustment in the Audacity system to individually adjust stereo levels when using the USB input?
That sounds rather odd. What is the make/model of the device?
Audacity does very little in “real time”. Essentially, when recording, Audacity records the audio that it receives without modifying it. Modifying the audio is something that you can do in Audacity after recording.
If you want / need complete control of each audio channel separately, split the stereo track into two tracks using the “Split Stereo Track” option in the track menu (http://manual.audacityteam.org/o/man/track_drop_down_menu.html).
More information about splitting and joining tracks is here: http://manual.audacityteam.org/o/man/splitting_and_joining_stereo_tracks.html