Effects unit

An effects unit, effects processor, or effects pedal is an electronic device that alters the sound of a musical instrument or other audio source through audio signal processing.

Common effects include distortion/overdrive, often used with electric guitar in electric blues and rock music; dynamic effects such as volume pedals and compressors, which affect loudness; filters such as wah-wah pedals and graphic equalizers, which modify frequency ranges; modulation effects such as chorus, flangers and phasers; pitch effects such as pitch shifters; and time effects such as reverb and delay, which create echoing sounds and emulate the sound of different spaces.