Wah-wah: A wah-wah pedal creates vowel-like sounds by altering the frequency spectrum produced by an instrument—i.e., how loud it is at each separate frequency—in what is known as a spectral glide or "sweep".[70] The device is operated by a foot treadle that opens and closes a potentiometer. Wah-wah pedals are often used by funk and rock guitarists.[71]