Understanding the coherence properties of musical vibrato signals

Abstract

In the field of optics, coherence theory is used to characterize the relative correlation of optical fields at different points in space and time. While this framework has found fewer applications in acoustics outside of an imaging context, recent work has explored the possibility of characterizing rooms and other acoustical systems based on the coherence properties of naturally occurring reverberant sounds. Additionally, the cross-correlation functions used in coherence theory also underly many auditory perceptual models which leverage interaural correlations to estimate interaural time differences (ITD) used in sound localization. In these contexts, musical vibrato constitutes an important type of partially coherent signal. The quasiperiodic frequency, and often amplitude, modulation inherent to natural vibrato serves to reduce the coherence time of the sound, while being defined by a small set of relatively constant control parameters. This presentation will describe the relative impact of vibrato performance parameters, including vibrato rate and depth, on the coherence properties of the signal for various instruments. Analysis of recorded instrument samples will be compared predictions from a sinusoidal synthesis model for both the dry and reverberant cases. Finally, the potential for characterizing other musical systems, such as instruments, using coherence theory will be explored.