Vibrato and tremolo are often confused — and not just by musicians, but by manufacturers as well. The tremolo arm on your favorite guitar, for example, is actually a vibrato arm. As modulation effects, both produce a similar sense of movement and rhythm, but the way in which they do it is completely different.
Vibrato is a modulation effect that varies pitch. As the pitch cyclically goes higher and lower in response to the modulation, a sense of movement and rhythm are created, and the variations in pitch can also can make the notes seem stronger and richer. This is actually the way that “tremolo” bars work, despite their name.
Tremolo is also a modulation effect, however in this case the movement and rhythm is created by varying the amplitude, or volume, of the signal. Tremolo is particularly useful for creating percussive shuddering or stuttering, as well as gentle or intense pulsating effects.
Tremolo effects can be found on many amps, such as some Marshalls, Fenders, and Voxes, as well as in stompboxes and effects devices. True vibrato effects are available in certain stompboxes and effects processors, but rarely built-into amps.
So the next time you’re looking for the perfect effect to create a sense of undulating rhythm and motion, if you want a more warbly, “underwater” pitchy sound, go for vibrato. If you want a more staccato stuttering or pulsating effect, go for tremolo!