Tremolo: A tremolo effect produces a slight, rapid variation in the volume of a note or chord. The tremolo effect should not be confused with the misleadingly-named tremolo bar, a device on a guitar bridge that creates a vibrato or pitch-bending effect. In transistorized effects, a tremolo is produced by modulating an instrument's audio signal with a sub-audible carrier wave in such a way that generates amplitude variations in the sound wave. Tremolo effects are built-in effects in some vintage guitar amplifiers. The guitar intro in the Rolling Stones' "Gimme Shelter" features a tremolo effect.