Timbre is determined by the relative amplitudes of partials, not their frequencies alone

Evidence

Timbre is the third of three executive summaries of sound provided to our consciousness, after pitch and loudness. Timbre is what is different about a trumpet and a clarinet when they (separately) play a 220 Hz tone at the same loudness. Like all sensory functions, timbre is a complex, difficult to measure, psychophysical phenomenon. As with the sense of taste, there are subtleties and there are also connoisseurs. Impressions of timbre depend on context and experience. We shall try to sidestep these nuances and take a simplistic view: timbre is a kind of executive summary of the distribution of amplitudes of the various partials in a complex tone. Two sounds having all the same frequencies present but differing in amplitude have a different timbre. — Eric J. Heller, Why You Hear What You Hear- An…, 2201

Categorization

• DEFINE: Defines timbre as the executive summary of partial amplitude distribution — the key working definition for the chapter.
• XREF: connects to: Color analogies naturally describe timbre, whose acoustic basis is overtones — David Howard, Jamie Angus, coustics and Psychoacoustics, 1452