An envelope filter effect pedal is a type of audio effect that alters the sound of an instrument based on the dynamics of the player’s performance, specifically how loudly or softly they play. It works by using an envelope follower, which tracks the amplitude (volume level) of the signal and controls a filter that modulates the sound accordingly. The result is a distinctive sound where the filter’s cutoff frequency is swept up or down in reaction to the player’s attack, creating a “wah” or “quack” effect.

Envelope filters are commonly used in genres like funk, electronic, and rock to add a dynamic, expressive quality to the sound. The pedal can produce a range of tones, from subtle, smooth sweeps to more pronounced, percussive filter effects. The effect is most noticeable when playing with strong dynamics, such as heavy picking or fingerstyle playing, as the intensity of the filter changes in real-time. Some popular envelope filter pedals include the Electro-Harmonix Q-Tron and the MXR Envelope Filter, both of which allow players to shape the effect’s response with adjustable sensitivity, attack, and filter range for greater tonal control.