Many of my compositions, especially my recent electroacoustic works, feature what I call defining sounds -- pitch or rhythmic motives, sonorities or chords that are associated with a unique or particular timbre and that recur prominently in varied form and different contexts during a work. These defining sounds are intended to impart a particular "energy level," quality of movement and expressive "character" or "tone" to the work. I have been asked on several occasions to define this term more fully, and to illustrate how these defining sounds are created and combined, and so am providing a summary (perhaps in more detail than anyone wishes) and 19 mp3 audio examples here.
In my two-movement composition Diaspora for soprano and computer generated sounds the most prominent of these defining sounds within the computer part consist of progressions of vocal-like sonorities or "chords" that are derived from generic vocal samples, such as this source bass choir tone : example 1
Several steps were involved in processing these rather bland source vocal tones and transforming them into timbral/pitched thematic material with a more distinctive and memorable quality of expression.
(1) First the samples were run through a phase vocoder algorithm, which, among other things, I used to eliminate some of the frequencies (harmonics) present within the original tones. Often, the fundamental frequency, and the higher frequencies, are eliminated, leaving only six, seven or eight surviving frequencies from the middle of the original spectrum. Sometimes, the remaining frequencies also are shifted by a constant factor (e.g. by adding 100 hertz to each frequency), which alters the original harmonic or inharmonic ratios between these frequencies. (Note that that shifting all of the frequencies in a spectrum by a constant amount, as here, changes the timbre, producing a result quite different from shifting all frequencies by a constant ratio, which produces a simple pitch transposition.) The result, to my ears, is somewhat like a "shadow" of the source sound, retaining some of the recognizable qualities of the original tone but giving it a new musical definition or "feel."
Here are two variants of the source bass choir tone that were created in this fashion. In example 2 the original sample remains recognizable. In example 3, however, upward frequency shifting of the harmonics creates a thinner, "more airy" timbre.
A salient feature of both examples is an ambiguous or paradoxical aural quality that I find intriguing. Because some of the harmonics of the source vocal tone have been removed, and the amplitude and/or frequency relationships of the remaining partials have been recast, the frequencies no longer fuse as readily into a single perceived tone, and we are more aware of the individual frequency components within the two processed variants. One might hear or interpret either of these variants as a timbre or as a "chord." Jean-Claude Risset first explored such "timbre/chord" aural paradoxes forty years ago.
(2) The next step in the creation of the defining vocal sounds within Diaspora was to mix together groups of two or three processed variants like the two above, usually with pitch transpositions, in order to fashion more complex or richer composite chord/timbres, like this example 4.
(3) Finally, during the composition of Diaspora, I combined groups of two, three or more of these composite timbral/pitch sonorities, such as the fourth example above, to form progressions, like this example 5 and this example 6. These fourth and fifth examples exemplify the way in which the defining vocal sounds are heard in Diaspora. To my ears these progressions have a hollow, drifting or rootless, tenuous or rarefied quality that defines one of the principal affective musical qualities of the composition.
In addition to the hollow vocal-like progressions discussed above several other groups of defining sounds are employed in Diaspora. The contrasts, similarities, interplays and movement between these collections is vital to the structure and expressive content composition. Some of the defining sounds are employed in both movements, delineating elements that characterize the piece as a whole, while others are used only (or else primarily) in one of the movements to underscore contrasts in structure and expressive quality between the two movements.
While this discussion has focussed on the computer part to Diaspora, the solo soprano part similarly incorporates defining motivic ideas, which often are associated with particular vocal timbral resources or performance techniques, and sometimes are paired with particular defining sounds within the computer part.
Terms such as "associated" (or "paired with") and "vairants" have appeared frequently within this discussion, as have subjective descriptive terms such as "hollow,""dense" and "metallic." The defining sounds in Diaspora often are varied and developed simultaneously in groups of two or three ideas rather than individually, and then are further varied or developed in new combinations ("associations") at later points in the work. My intention is that through these changing associations (or linkings) common or similar elements and relationships among these defining sounds become increasingly apparent over time, and clarify the defining ideas (the structure and qualities of expression) of the work as a whole.
The following 30 second excerpt from the computer part to the second movement illustrates this "coming together," layering and simultaneous development
of several of the defining sounds discussed above: example 19
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