Tristimulus values

The tristimulus values of a color are the amounts of the three primary colors in a three-component additive color model needed to match that test color. The tristimulus values are most often given in the CIE 1931 color space, in which they are denoted X, Y, and Z.

Audio tristimulus
By analogy with the above, tristimulus parameters for audio have been proposed and used, based on the strengths of the harmonics in a sound.