Effluvium

Paul Riker, Music Composition

Sound is produced by a vibrating source and transmitted, via sympathetic vibrations in the molecules of the air, to our ears. We interpret the quality, or timbre, of a sound by its specific vibration pattern. This complex pattern, called the waveform, can be understood as a combination of many simple waves, called partials, which unite to create an overall impression of the sound. There are an infinite number of possible mathematical relationships between the constituent partials of the total waveform. One such relationship occurs when the frequencies of the partials are all multiples of a single, lower frequency. Under these conditions, the partials are said to be harmonic partials, and their common denominator is called the fundamental. An interesting property of harmonic partials is that if a group of partials is sounded, even in the absence of their fundamental source vibration, they cause the fluid of the ear to vibrate as if the fundamental HAD been sounded. Furthermore, our ears will not perceive the individual partials, but only the fundamental frequency, which exists only as a ghostly result of these higher frequencies.

In the world of computer synthesis, it is possible to construct complex sounds by manipulating individual partials. One of my recent projects was designed to explore the fuzzy boundary between individual partial perception, and fundamental perception. This phenomenon, sometimes called effluvium, occurs when a listener's ear mechanism transitions between interpreting its input as several higher frequencies and a single low frequency. My piece, called Effluvium, is a musical exploration of the phenomenon.