High-resolution measurement and simulation of sound source directivity

Participants: Esteban Maestre, Gary P. Scavone

Collaborator: Julius O. Smith

Period: 2018 - ongoing

Methods are proposed for measuring and simulating the free-field, frequency-dependent directivity of linear sound sources for use in real-time within geometric acoustic environments. Measurements are obtained by means of a high-resolution microphone array providing 4320 measurement on a sphere around the sound source. The simulation methods are based on using minimum-phase measurements to design a state-space filter presenting matrices of mutable size and time-varying coefficients. This allows the interactive simulation of a time-varying number of radiated sound wavefronts, each toward a time-varying direction. This filter structure, which enables convolution-free, low-latency simulation on perceptual frequency resolutions, can be applied to both directive sources and directive receivers.

In the context of a research project dealing with recreating the sound of the famous Stradivari Messiah in virtual reality, a first application involves reproducing the radiation characteristics of real acoustic violins to design virtual replicas playable through silent electric fiddles.

In a subsequent study, the methods are further developed and applied to modeling the directivity of a violin body and a clarinet air column from minimum-phase experimental acoustic data. With applicability in sound synthesis and/or auralization within virtual environments where sound sources change position and orientation dynamically, techniques are proposed for modeling and simulating directivity profiles on perceptual frequency axes with alternatives for representing directivity on a per-vibration-mode basis while incorporating relative phase terms or by reduced-order efficient representations comprising separate components for the signature resonant structure and the associated directivity on an adjustable frequency resolution.

The complete set of violin and clarinet (6 different fingerings) measurements described in the paper above are being made publicly available for download here. Each set is stored as Matlab formatted data in a '.mat' file below, and comprises an array of 4320 frequency responses (positive-frequency axis only), two arrays of 4320 angles each respectively indicating the azimuth and inclination (in rad) corresponding to each frequency response, and a scalar indicating the sampling rate (in Hz). For further information on the measurements, please read the paper above. To document the use of these data in your work, please cite the paper above.