its a knob that will apply an insertion effect(press and hold it for about 3 seconds and the screen will automatically jump to 89 insertion effects), but when you enter a 16-track sequencer and wanna start a song from scratch it doesn`t let an M-FX to any track(but every track has a CHORUS, REVERB, and DELAY). When I play live I like to use an effect called 4-tap delay.