Modwheel

The modwheel (short for modulation wheel) is a physical controller found on most MIDI keyboards or synthesizers, usually located to the left of the keys. By default, it controls modulation — such as vibrato, tremolo, a filter, or any other assigned parameter. It allows for adding expression and real-time movement while playing, without needing to use a mouse or software knob. On modern synths, the modwheel can be mapped to virtually any parameter.