Why does a clarinet’s sound differ from that of an oboe? What makes a high C on a piano sound different than when it’s produced by a soprano? Timbre is the answer. It’s everything about the sound other than pitch that makes it unique.
Some folks at Georgia State University have a handy but old web page up that breaks down fairly well the formal components of Timbre. They explain that “The primary contributers [sic] to the quality or timbre of the sound of a musical instrument are harmonic content, attack and decay, and vibrato.” That more or less agrees with what Wikipedia has to say on the subject.
Harmonic content refers to the collection of frequencies at work to produce a sound. Harmonic content always includes a fundamental frequency (the note being played or sung or produced) and multiples of that frequency – it’s the various multiples that make the difference. Concert “A” is usually 440 hertz, for example, and any given instrument, along with vibrating at 440 hz, also produces sounds at the 880, 1320, and on up multiples of the base frequency. Violins have some very interesting harmonic properties; very lightly touching the string and bowing will produce tones of very high frequencies, for example.
Attack and decay, the second component of Timbre, got me awfully excited just by the name. It refers to the nature of how quickly a sound rises to its full amplitude, and how quickly the amplitude diminishes back to nothing. Plucking a string creates a slower attack than does striking a drum with a drumstick, for example. When a string is plucked, the decay represents how long it takes the string to stop producing a sound. So a decay rate for a cymbal, for example, is very long, whereas the decay rate for the low battery beep coming out of your smoke detector it is very short.
Vibrato is a feature of tones with which most people have some familiarity. The human voice often shines best when some regular rising and falling of the pitch around a base note happens. String and wind instruments often employ vibrato as well.
So you put them together – harmonic content, attack and decay, and vibrato – and you have the timbre of the music. To my mind, there’s no avoiding the je ne sais quoi component of timbre – Wikipedia cites Dixon Ward writing in 1970, who notes that timbre is “…the psychoacoustician’s multidimensional waste-basket category for everything that cannot be labeled pitch or loudness.” Alrighty then!
Thanks for reading.