Nathan Wolek (Stetson University, USA)
In Formalized Music (1963/1992), Iannis Xenakis proposed a method of using sonic grains to synthesize original sounds. His musical application of Gabor’s (1947) theory of “acoustical quanta” has since spawned a variety of electronic and computer music techniques chronicled by Curtis Roads in Microsound (2001). The most well known among these techniques are granular synthesis and granular processing.
In developing his proposal, Xenakis gave consideration to the limits of human auditory perception. He wanted to ensure the grains would not fall below the minimum duration and intensity that a listener could perceive. Xenakis also employed Fletcher-Munson equal-loudness contours as the basis for his screens. Although future research and development of granular techniques would continue to demonstrate an awareness of perceptual issues, direct empirical study of how listeners perceive granular sounds is missing from the literature.
The current author designed a series of three experiments to investigate how listeners perceive differences between granular processing examples. Stimuli were produced using specific program settings to process two distinct sound sources. In each experiment, at least twenty participants were asked to rate the similarity of each possible pair of stimuli including identity pairs that existed among these stimuli. The author then used multidimensional scaling (MDS) to develop a graphical representation of the perceptual organization exhibited by participants.
Differences between stimuli included the processed sound source and settings for the grain duration and grain period parameters. Visual analysis of the MDS solution showed that participants clearly distinguished between the two sound sources. Processing descriptors based primarily on a review of the literature were tested for correlation to the MDS dimensions. The author’s analysis will highlight the significance of three processing features: (1) a base-2 logarithmic scaling for differences in grain duration, (2) the minimum and maximum boundaries for randomized grain durations, and (3) the mean value and total deviation for randomized grain periods.
The findings were used to inform the design of a new graphical user interface (GUI) for granular processing. The resulting GUI helped to verify this study's conclusions by successfully demonstrating their practical application to software development. The author will demonstrate the GUI’s unique controls for managing randomization and its feedback display for monitoring differences between the control input and audio output.
The author will conclude by addressing future directions in which this research may continue. Processing differences for the current experiments were limited to grain duration and grain period in order to provide a necessary focus. Additional parameters for testing in future experiments will be identified, as well as experimental methods besides MDS that may be used to approach this same inquiry and strengthen the current study’s findings.
Nathan Wolek recently completed his Ph.D. in Music Technology at Northwestern University. His work encompasses multimedia performance, audio installation art, signal processing techniques, and the analysis of electro-acoustic music. His software development includes VST plug-ins and Max/MSP externals that are used by artists around the world. He has studied under Gary Kendall, Amnon Wolman, Virgil Moorefield, Michael DeMurga and Kari Juusela. Nathan has taught at Columbia College Chicago, Northwestern University, University of Hawaii at Manoa and has recently been appointed Assistant Professor of Music Technology at the Stetson University.