In the Audio Track Mixer, I have opened the upper half where the FX inserts are located. There are 3 blank areas to do this. The bottom blank area contains a circular icon and, having got this thing activated once before. I know that this is where I can, for instance, bump up the gain for that track.
But I've forgotten how to activate it this knob/controller, Can you please remind me?
I have been searching for about 45 minutes both here and Google and the Adobe site.