The means by which the organist varies the opening of the swell shutters, to achieve musical dynamics (louder or softer). On a theatre organ, the swell pedals are ‘balanced’, i.e. they stay in whatever position they are left. To open the swells, the pedal is moved towards the horizontal and to close the swells, towards the vertical.
The swell pedals are located in front of the pedalboard.
Small organs with only one chamber may have a single swell pedal; normally there is one pedal for each chamber and on larger instruments a master pedal to which the other pedals may be connected electrically, thus allowing all swells to be operated as one. A small button may be seen on some swell pedals; this is to operate the dampers (sustain) of an organ piano, if fitted.
To the right (conventionally) of the swell pedals may be another pedal, the crescendo pedal, which puts stops on gradually.