TIMBRE

also called Timber, quality of auditory sensations produced by the tone of a sound wave. The timbre of a sound depends on its wave form, which varies with the number of overtones, or harmonics, that are present, their frequencies, and their relative intensities. The illustration shows the wave form that results when pure tones of frequencies 100, 300, and 500 hertz (cycles per second) and relative amplitudes of 10, 5, and 2.5 are synthesized into a complex tone. At the right is the resultant of the three sine curves when their ordinates are added point by point along the time scale. In equation form, the amplitude y of the wave form at any time t would be represented by y = 10 sin (2p 100t) + 5 sin (2p 300t) + 2.5 sin 2p 500t. The timbre of this form would be recognizable and different from all others having a fundamental tone of 100 hertz. In music timbre is the characteristic tone colour of an instrument or voice, arising from reinforcement by individual singers or instruments of different harmonics, or overtones (q.v.), of a fundamental pitch. Extremely nasal timbre thus stresses different overtones than mellow timbre. The timbre of the tuning fork and of the stopped diapason organ pipe is clear and pure because the sound they produce is almost without overtones. Timbre is determined by an instrument's shape (e.g., the conical or cylindrical pipe of a wind instrument); by the frequency range within which the instrument can produce overtones; and by the pattern of onset, growth, duration, and decay (envelope) of the instrument's sound. The timbre of spoken vowels or of a singing voice varies with the openness or constriction of the head-and chest-resonating areas used.