Timbre is a multi-dimensional percept that requires a feature list rather than a single number to describe

Timbre is what distinguishes two sounds of the same pitch, loudness, and duration. It cannot be described by a single value; it requires a multi-dimensional property list. Key dimensions identified by psychoacoustic studies include spectral centroid (centre of mass of spectral energy), attack envelope, and the time-varying distribution of spectral energy. Periodic sounds are additionally distinguished by which harmonics are present and their evolution. In electronic music, traditional physical-production cues are absent, making timbre design a primary creative concern. The spectral centroid correlates strongly with perceived brightness.

Examples

A piano, clarinet, and trumpet playing middle C at the same SPL are easily distinguished by timbre despite identical pitch and loudness. Auto-Tune exploits the separability of pitch from timbre.

Assessment

Name two psychoacoustic features that recur in studies of what distinguishes sounds’ timbres. Why can timbre not be captured in a single number the way pitch and loudness approximately can?