Gregory J. Sandell
Exp. Psychol., Univ. of Sussex, Brighton BN1 9QG, UK
Concurrently sounding timbres (two or more instruments playing on the same or different pitches) sometimes yield unexpected qualities of sound which are exploited in orchestration. A model simulating spectrum analysis by the human auditory periphery is used to explore the differing contributions of individual instruments to the sum sound. Signals are passed through a bank of overlapping bandpass filters whose center frequency spacing corresponds to equal physical distances along the basilar membrane. Thus sinusoidal components do not fall into single ``bins'' as in a Fourier analysis, but rather spread excitation over a large number of channels. Some partials are resolved in separate channels while other partials are processed in a single channel with others, leading to interactions that determine the overall timbre of the combination. Sampled musical instrument tones are combined into concurrent arrangements and analyzed with the method.