P. Huang’s scientific contributions

An acoustically transparent, configurable microphone array with omnidirectional elements, designed for room acoustics analysis and synthesis, and archaeological acoustics applications, is presented. Omnidirectional microphone elements with 2 mm-diameter capsules and 1 mm-diameter wire mounts produce a nearly acoustically transparent array, and provide a simplified mathematical framework for processing measured signals. The wire mounts are fitted onto a 1.6 cm-diameter tube forming the microphone stand, with the microphones arranged above the tube so that acoustic energy can propagate freely across the array. The wire microphone mounts have some flexibility, and the array may be configured. Detachable arms with small speakers are used to estimate the element positions with an accuracy better than the 2 mm microphone diameter.

A series of psychoacoustic experiments were carried out to explore the relationship between an objective measure of reverberation echo density, called the normalized echo density (NED), and subjective perception of the time-domain texture of reverberation. In one experiment, 25 subjects evaluated the dissimilarity of signals having static echo densities. The reported dissimilarities matched absolute NED differences with an R2 of 93%. In a 19-subject experiment, reverberation impulse responses having evolving echo densities were used. With an R2 of 90%, the absolute log ratio of the late field onset times matched reported dissimilarities between impulse responses. In a third experiment, subjects consistently reported breakpoints in echo pattern character at NEDs of 0.3 and 0.7.

Loss and diffusion elements are proposed for a digital waveguide mesh reverberator. The elements described are placed in the interior of the waveguide mesh, and may be viewed as modeling objects within the acoustical space. Filters at internal scattering junctions provide frequency-dependent losses, and control over decay rate. One proposed design method attenuates signals according to a desired reverberation time, taking into account the local density of loss junctions. Groups of one or several adjacent scattering junctions are altered to break up propagating wavefronts, thereby increasing diffusion. A configuration which includes these internal elements offers more flexibility in tailoring the reverberant impulse response than the common waveguide mesh construction where loss and diffusion elements are uniformly arranged solely at the boundaries. Finally, such interior decay and diffusion elements are ideally suited for use with closed waveguide structures having no boundaries, such as spherical or toroidal meshes, or meshes formed by connecting the edges or surfaces of two or more meshes.

Digital waveguide networks (DWN) are known as a methodology to simulate spatially distributed systems, such as reverberators (room simulation) and resonators of musical instruments. This paper is an overview and study on the application of DWNs to simulate acoustic spaces for room rendering, including auralization. The methods discussed combine the principles of digital waveguide meshes, image source models, reverberation algorithms, and HRTF-based rendering. Examples are given on synthesizing room responses for simple room geometries, and the possibilities of fitting the models to real room responses are discussed. System performance is discussed from the point of view of real-time virtual acoustics.