Using Physically-Based Models and Genetic Algorithms for Functional Composition of Sound Signals, Synchronized to Animated Motion
GEORGE WASHINGTON UNIV WASHINGTON DC DEPT OF ELECTRICAL ENGINEERING AND COMPUTER SCIENCE
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We represent sound signals as general functional compositions, called Timbre Trees. Externally these are LISP-like expressions, internally they are implemented as C data structures. Nodes of the tree can be arithmetic operations, analytic functions or noise generators. Vectorized operations are provided for compact expression of additive spectral synthesis, and convolution operators for modeling acoustical environment reverberation within the same structure. A similar script language is also used to define three-dimensional animated motion. Simulation determines collisions and other sound-causing interactions between objects, and generates timbre trees from which exactly synchronized soundtracks can be prepared. Heuristic physically-based vibration models are used to determine the timbre of simulated instruments. Because it is often difficult to find the right composition of functions and their parameters that make up a desirable sound, we use genetic algorithms to mutate timbre trees and allow the user to guide their evolution. Time-variable parameters allow continuous metamorphosis between geometric objects and their sounds. Using this methodology, we have produced a variety of convincing animated scenes.