The Technology of Wah Pedals

The stock "wah" pedal has been around since at least the early 60's. This thing produces a distinctive tone that is well loved by the expressive guitarist. What a wah does is clear - it is either a bandpass filter or an overcoupled lowpass filter that exhibits a resonant peak just at its lowpass rolloff frequency. The resonant peak can be moved up and down in frequency by the player, and this makes for a striking emulation of the human voice making a "waaaah" tone, or its tonal inverse, "aaaooow".