Vibrato and tremolo are expressive effects that are applied both naturally and electronically by vocalists, instrumentalists, and sound designers. These terms are often mistakenly used to describe the other effect. This is what the words mean and how the effects differ from each other.

In a nutshell

Vibrato is fluctuation of the pitch (frequency) of a sound. Tremolo is fluctuation of the volume of a sound. The sound can be a single note (like a voice), or a group of notes (like a guitar chord).

Vibrato

Vibrato is “frequency modulation”. Imagine an opera singer, holding out a long note. The pitch wavers up and down, centering on a particular note. It can be a fast modulation or slow.

Electric guitarists may be familiar with the “whammy bar” that you grab to bend the pitch of a note. This produces vibrato as well. However, here’s where we get into some of the confusion of the names of these two terms. In the 1950s, Leo Fender called this a “tremolo bar”, which is a misnomer.

the metal arm that extends from the bridge of the guitar produces vibrato on struck notes when moved

Tremolo

Why isn’t a whammy bar really a “tremolo” bar? It’s because tremolo is “amplitude modulation”. Imagine taking a volume knob of an old radio and turning it up, then down, then up, down, etc. That’s tremolo. Since a whammy bar changes the pitch, it’s vibrato. An amplifier or stombox effect of “tremolo” brings the volume of a sound up and down.

Side note: There is an alternate definition of "Tremolo" in classical music meaning a rapid repeating of a note, which is especially prevalent in string orchestras.

Here’s a good explanation with audio examples by Scott Grove and Groovy Music Lessons:

What music terms would you like to know more about? Ask away!