pedal modes

A wah-wah pedal, or simply wah pedal, is a type of effects pedal designed for electric guitar that alters the timbre of the input signal to create a distinctive sound, mimicking the human voice saying the onomatopoeic name "wah-wah". The pedal sweeps a band-pass filter up and down in frequency to create a spectral glide. 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, and out of the instrument's bell. This was later simulated with electronic circuitry for the electric guitar when the wah-wah pedal was invented. It is controlled by movement of the player's foot on a rocking pedal connected to a potentiometer. Wah-wah effects may be used without moving the treadle as a fixed filter to alter an instrument’s timbre (known as a “cocked-wah”), or to create a "wacka-wacka" funk-styled rhythm for rhythm guitar playing.
An auto-wah pedal uses an envelope follower to control the filter instead of a potentiometer.

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