A wah pedal is a foot-controlled bandpass filter or a lowpass filter that exhibits a resonant peak just at its roll-off frequency. The resonant peak can be moved up and down in frequency by the player by means of a foot pedal, which makes for a striking emulation of the human voice making a “waaaah” tone (or its tonal inverse, “aaaooow”).
Several kinds of circuits have been used through the years to produce the wah sound. One of the originals was the Vox-style inductor-based wah circuit. Other common wah circuits employed notch filters or op-amp active filters.
