ABSTRACT – 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. 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.

• Download Slides in PDF – 1.2 MB

• Download PDF file – 3.1 MB

ABSTRACT – Granular processing is a computer music technique that manipulates “grains” of sound to produce a variety of effects. Grains are produced by multiplying short segments of digital audio, typically lasting between 10 and 50 milliseconds, with an amplitude envelope of equivalent length. Software designed to produce granular processing effects often requires the user to manage multiple parameters that lack a clear connection to the audio output. A better understanding of how listeners perceive the processing output should yield insights into how the user interface could be simplified.

A series of three experiments was designed 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 the review of literature were tested for correlation to the MDS dimensions. This analysis revealed 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.

Between-subject variables relating to experience with electroacoustic music were also examined. However, the results of this secondary inquiry were deemed inconclusive overall based on the relationship between participants’ responses to pre-experiment questions and a priori operational definitions.

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 GUI features unique controls for managing randomization and a feedback display for monitoring differences between the control input and audio output.

Co-authors: Gary Kendall and Scott Lipscomb.

EXCERPT -Granular processing of sampled audio signals (Roads 1985; Traux 1987) is a technique that has experienced increased interest in recent years. This processing technique has origins in the work of Dennis Gabor and his concept of the acoustical quanta (Gabor 1947), which was developed in response to perceptual research findings. He asserted that, “it is our most elementary experience that sound has a time pattern as well as a frequency pattern (Gabor 1947, p. 591).” Although several software applications are now widely available for realizing granular processing effects (Roads and Alexander 1997; Behles, Starke and Roebel 1998; van der Schoot 1999; Rolfe and Keller 2000), these programs have done little to clarify the perceptual connection between interface controls and audio output, a problem that has persisted since the first computer implementation was reported twenty-five years ago (Roads 1978). A better understanding of how the audio output is perceived is a necessary precursor to the development of a simplified interface that would require the computer “to interpret how to approximate a desired result” (Roads 2001a, p. 27).

In order to further this goal of understanding the perception of granular processing better, the author has conducted a series of three experiments based on models found within studies of musical timbre (Grey 1977; Wessel 1979; Kendall and Carterette 1991; Iverson and Krumhansl 1993). These studies have employed a method of exploring the topic using a similarity-scaling task. Subjects would listen to a series of pairs of sounds, rating the similarity of each pair member to the other while moving through all possible couplings of the stimuli. These similarity ratings were then averaged together and used as the basis for formulating a multi-dimensional scaling solution (Shepard 1962a, 1962b; Kruskal 1964a, 1964b). MDS uses these similarity ratings to produce a graphic representation of the relationships that exist within that data. Stimuli that are viewed as similar will be placed in close proximity to one another, while those viewed as dissimilar will be have a greater distances between them. The differences are represented in a single graphic plot of points representing the stimuli used. This seemed like an appropriate method to employ in our study, however we must emphasize that we are not attempting to draw connections between the results of our study and those found in timbre research. Our comparison is simply with their experimental methods.

• Download Paper in PDF – 428 kb