Tremolo is a modulation effect that varies the volume of a guitar signal at a controlled speed and depth, creating a pulsing or wavering sound. This effect is achieved by rapidly increasing and decreasing the amplitude, producing anything from a subtle, shimmery movement to a dramatic, choppy stutter. Tremolo was one of the earliest built-in amp effects, famously used in vintage Fender amplifiers. Modern tremolo pedals offer classic analogue circuits or digital flexibility with features like tap tempo and wave shape control. Popular tremolo pedals include the Boss TR-2, Fulltone Supa-Trem, and Strymon Flint, making it a favourite for surf rock, blues, indie, and experimental music.