The knobs can be adjusted by changing their values numerically, moving the sliders under the Individual Parameters, dragging around the edges of the knobs with your mouse in Custom Setup or, most easily, by using one of the audio effect presets.
Those options all work for me. Which audio effect are you not able to adjust?
I have checked on my versions 9 and 11 (french install) : as indicated by Steve, to use the
mouse for rotating, you have to position the pointer on the top of the button.
The movement of the mouse then turns the button without need to enter numeric values.
Checked on the window : audio mix (mixage audio), not on other effects.
Thanks to both Steve and JM.
I was trying a circular movement arround the knob without much success.
Putting the mouse a the top of the knob and going left or right works.