Timbre is defined as the residual difference once loudness, pitch, and duration are matched

Evidence

There is no subjective rating scale against which timbre judgments can be made, unlike pitch and loudness which can, on average, be reliably rated by listeners on scales from “high” to “low.” The commonly quoted American National Standards Institute formal definition of timbre reflects this: “Timbre is that attribute of auditory sensation in terms of which a listener can judge two sounds similarly presented and having the same loudness and pitch as being dissimilar” (ANSI, 1960). In other words, two sounds that are perceived as being different but which have the same perceived loudness and pitch differ by virtue of their timbre (consider the examples on track 62 of the accompanying CD). — David Howard, Jamie Angus, coustics and Psychoacoustics, 1451

Categorization

• DEFINE: ANSI’s formal definition of timbre as the residual attribute once loudness and pitch are matched is the canonical clarification of an otherwise intuitive term.
• XREF: Connects to the chapter heading’s focus on ‘deceiving the ear’ — timbre is what survives clever disguise of pitch and loudness.