ANA filter 1/2 control

very new to sound design guys and im using ANA to learn on as there is lots of good tutorials for me. I have 1 issue im really struggling to understand though. How does filter 1/2 (the big filter knob) work. What is it that it actually does. If i was not there everything would be great but i see it used and i just dont get it. If i have already cut out frequencies in filter 1 how does that filter seem to add sound…confused br
Thanks in advance