ASA/CAA '05 Meeting, Vancouver, BC

Music and Science Meet at the Micro Level:
Time-Frequency Methods and Granular Synthesis

Barry Truax - truax@sfu.ca
School of Communication & School for the Contemporary Arts
Simon Fraser University
Burnaby, BC Canada V5A 1S6
URL: www.sfu.ca/~truax

Popular version of paper 2aMU5
Presented Tuesday morning, May 17, 2005
Joint ASA/CAA Meeting, Vancouver, BC

Musical research over the last century has become increasingly entwined with the areas of acoustics, psychoacoustics, and electroacoustics. One of the most striking results has been to push the frontiers of models of sound and music to the micro level, what is generally termed microsound. At this level, concepts of frequency and time are conjoined by a quantum relationship, with an uncertainty principle relating them that is precisely analogous to the more famous uncertainty principle of quantum physics. A class of methods of sound synthesis and signal processing known as time-frequency models have their basis at this quantum level such that changes in a signal's time domain result in spectral alterations and vice versa. One such method, granular synthesis and the granulation of sampled sound, produces results by the generation of high densities of acoustical quanta called grains. Such a radical shift has profound implications for not only our models of sound design, but also for the compositional methods that emerge as well as the role of the composer in guiding complex processes. The paper will argue that these models are examples of a class of complex systems exhibiting emergent form that create a new form of virtual music instrument.

One of the results of granulation the technique is a dramatic alteration of the sound called "time stretching" which allows a sound to be prolonged by any factor with no resultant change in pitch. The inner properties of the timbre of the sound become more apparent to the ear; voice inflections are heard more as musical melodies, and extreme degrees of stretching make a sound resemble an environmental ambience. Another micro-level technique, called convolution, multiplies the spectra of two sound together. What this means is that when a sound recorded in a dry studio is convolved with the impulse response of a reverberant space (e.g., a recording of a balloon popping), the first sound appears to be in that reverberant space. Convolving the sound with itself also stretches it into a version that is half way between the original and the reverberant portion. These and other techniques give composers a new way of working from "inside" the sound.

Web references:
Granulation of Sampled Sound
Convolution