In music, timbre is the quality of a musical note which distinguishes different types of musical instrument. See also: formant of speech, singing, and musical instruments. This is why, with a little practice, you can pick out the saxophone from the trumpet in a jazz group or the flute from the violin in an orchestra, even if they are playing notes at the same pitch and amplitude. Timbre has been called the psychoacoustician's waste-basket as it can include so many factors.

Though the phrase tone color is often used as a synonym for timbre, colors of the optical spectrum are not generally explicitly associated with particular sounds. Rather, the sound of an instrument may be described with words like "warm" or "harsh" or other terms, perhaps suggesting that tone color has more in common with the sense of touch than of sight. People who experience synaesthesia, however, may see certain colors when they hear particular instruments.

The physical characteristics of sound which are used in the determination of timbre are spectrum and envelope, but psychoacoustics also plays an important and little-understood part.