Acoustic Communication and Compositional Techniques (review)

A newly released interactive double DVD-ROM Acoustic Communication & Compositional Techniques by Barry Truax is a compelling teaching tool for computer music theory and composition that uses text, images, and sound examples to explore micro-level sound. The juxtaposition of mixed media imparts a glimmer into the theoretical, compositional, and stunning influences that inspire Truax’s formidable work. The first DVD-ROM is organized into sections: Microsound and Granular Synthesis, Granulation of Sampled Sound, Karplus-Strong Resonators and Comb Filters, Convolution, and Analysis of Specific Pieces including Riverrun (1986/2004) and The Shaman Ascending (2004–05). The second DVD-ROM includes sections on Soundscape Composition and Acoustic Space and additional analyses of compositions by Mr. Truax including Pendlerdrøm (1997), Island (2000), Temple (2002), Dominion (1991), and Chalice Well (2009). Complementary Web sites hint at the content included on the DVD-ROMs ( www.sfu.ca/~truax/riverdvd.html and www.sfu.ca/~truax/scompdvd.html ). These DVD-ROMs succeed Mr. Truax’s CD-ROM entitled Handbook for Acoustic Ecology (1999).

The section on micro-level sound design begins with a diagram that relates the time domain and frequency domain with the Fourier transform and inverse Fourier transform connecting each domain. Mr. Truax states that at the level of micro-sound, time and frequency are interdependent and linked by an Uncertainty Principle defined as:

He relates this Uncertainty Principle to the Heisenberg Uncertainty Principle that states that certain pairs of physical properties, like position and momentum, cannot simultaneously both be precisely known; the more precisely one property is known, the less precisely the other can be known. Mr. Truax creates the analogy with the Heisenberg Uncertainty Principle to make the point that a change in the time domain results in a change in the resultant spectrum. A lecture or supplementary reading that clearly explains the concepts should support the potent content of these slides.

Mr. Truax juxtaposes the extremes of frequency and time pictorially, explaining that discrete frequency assumes that the Fourier analysis is performed on a signal that lasts forever, e.g., infinite time. An impulse in time can be precisely measured, but a Fourier analysis may result in a multitude of frequencies (e.g., infinite bandwidth). Following the graphic relationship of time and frequency, he provides a diagram from Dennis Gabor’s landmark 1947 article, “Acoustical Quanta and the Theory of Hearing.” The diagram, without citation, depicts a Gaussian envelope applied to a window of a Fourier transform that produces a Gaussian envelope for the real part (frequency) of an analysis. Finally, he correlates the range of human hearing to our capacity to distinguish individual grains when those grains are temporally spaced at a time interval of 50 msec or more. As the grains become more closely spaced in time, the discrete events fuse into a complex timbre.

Granular synthesis is presented first historically, then in the context of the grain itself and the grain envelope. Various grain envelopes are presented visually, as well as three common types of granular synthesis: quasi-synchronous, asynchronous, and pitch-synchronous. There are 15 sound examples that increase in difficulty from a sinusoidal granular texture to phonemes that progress from a synchronous to asynchronous texture. These examples incrementally change variables such as frequency range, duration, and delay so that the listener can readily perceive the effect of specific variables on the resultant timbre.

Granulation of sampled sound is briefly defined as a technique that divides the (sampled) sound into short enveloped grains of 50-msec duration or less, and reproduces them with densities ranging from several hundred to several thousand grains per second. Mr. Truax has effectively used granulation of sampled sound through the development of his PODX system. Granulation of sampled sound is used in many of his compositions, such as The Wings of Nike (1987) and Tongues of Angels (1988...