Timbre Space as a Musical Control Structure

Research on musical timbre typically seeks representations of the perceptual structure inherent in a set of sounds that have implications for expressive control over the sounds in composition and performance. With digital analysis-based sound synthesis and with experiments on tone quality perception, we can obtain representations of sounds that suggest ways to provide low-dimensional control over their perceptually important properties. In this paper, we will describe a system for taking subjective measures of perceptual contrast between sound objects and using this data as input to some computer programs. The computer programs use multidimensional scaling algorithms to generate geometric representations from the input data. In the timbral spaces that result from the scaling programs, the various tones can be represented as points and a good statistical relationship can be sought between the distances in the space and the contrast judgments between the corresponding tones. The spatial representation is given a psychoacoustical interpretation by relating its dimensions to the acoustical properties of the tones. Controls are then applied directly to these properties in synthesis. The control schemes to be described are for additive synthesis and allow for the manipulation of the evolving spectral energy distribution and various temporal features of the tones. Tests of the control schemes have been carried out in musical contexts.* Particular emphasis will be given here to the construction of melodic lines in which the timbre is manipulated on a note-to-note basis. Implications for the design of human control interfaces and of software for real-time digital sound synthesizers will be discussed.