A sub effect, often referred to as a sub-octave, adds a lower-pitched signal beneath the original guitar tone, usually one or two octaves down. This creates a thicker, bass-heavy sound, making it especially useful for adding depth to riffs, solos, or even replacing a bass guitar in certain settings. Sub effects are commonly found in octave pedals and synth-style effects, with some offering multiple layers of octaves for an even bigger sound. They are widely used in rock, funk, and experimental music. Popular sub pedals include the Electro-Harmonix POG series, MXR Sub Octave Bass Fuzz, and Boss OC-5, all of which allow guitarists to achieve deep, earth-shaking tones.