A wah-wah pedal (or just wah pedal) is a type of guitar effects pedal that alters the tone of the signal to create a distinctive effect, mimicking the human voice. The pedal sweeps the peak response of a filter up and down in frequency to create the sound (spectral glide), also known as "the wah effect." The wah-wah effect originated in the 1920s, with  trumpet or trombone players finding they could produce an expressive crying tone by moving a mute in the instrument's bell. This was later simulated with electronics for the electric guitar, controlled by movement of the player's foot on a rocking pedal connected to a potentiometer. Wah-wah effects are used when a guitarist is soloing, or creating a "wacka-wacka" funk styled rhythm.