Timbre distinguishes sounds sharing pitch, loudness, and duration.

Evidence

The tonal colour, or timbre, is a multidimensional psychoacoustic measure. When two sounds have the same pitch, loudness, and duration, timbre is what makes one particular musical sound different from another. For example, the same musical notes played by a piano and a trumpet are easily distinguished by listeners as being different. The best physical explanation for this difference comes from the spectrum and its variation with time. — Ville Pulkki, Matti Karjalainen, Communication Acoustics- An…, 1179

Categorization

• DEFINE: Classic definition of timbre in terms of what remains after pitch, loudness, and duration are matched.
• XREF: connects to: Timbre is judged subjectively with no right answer, unlike pitch or loudness — David Howard, Jamie Angus, coustics and Psychoacoustics, 1505