Is it possible to add an effect on the combined result of all the stacked tracks?
In my situation I would like to apply levels on the result of the difference between 2 tracks, so I can see more clearly that difference. If I apply the levels to a track, it will not accentuate the difference but rather change result completely.

My apologies, I just found that I just have to click on Master and it opens the master effects which does exactly that. I think I just broke my record for the time between I post a question and find the answer.