FIL2 and FIL1 buttons

Hello. What is the function of the FIL2 and FIL 1 buttons in the filters. My first idea is that the two filters are then connected in series, but my ear cannot detect it. Or maybe something else is going on? Thank you for your help.

Yeah it’s like in series. Those buttons are inputs to the filter. If FIL 1 is selected on filter 2 then filter 1 is routed into filter 2 instead of to the effects.

Thank you from a French user