Realistic modeling of reverberant sound in 3D virtual worlds provides users with important cues for localizing sound sources and understanding spatial properties of the environment. Unfortunately, current geometric acoustic modeling systems do not accurately simulate reverberant sound. Instead, they model only direct transmission and specular reflection, while diffraction is either ignored or modeled through statistical approximation. However, diffraction is important for correct interpretation of acoustic environments, especially when the direct path between sound source and receiver is occluded.The Uniform Theory of Diffraction (UTD) extends geometrical acoustics with diffraction phenomena: illuminated edges become secondary sources of diffracted rays that in turn may propagate through the environment. In this paper, we propose an efficient way for computing the acoustical effect of diffraction paths using the UTD for deriving secondary diffracted rays and associated diffraction coefficients. Our main contributions are: 1) a beam tracing method for enumerating sequences of diffracting edges efficiently and without aliasing in densely occluded polyhedral environments; 2) a practical approximation to the simulated sound field in which diffraction is considered only in shadow regions; and 3) a real-time auralization system demonstrating that diffraction dramatically improves the quality of spatialized sound in virtual environments.

A difficult challenge in geometrical acoustic modeling is computing propagation paths from sound sources to receivers fast enough for interactive applications. This paper describes a beam tracing method that enables interactive updates of propagation paths from a stationary source to a moving receiver in large building interiors. During a precomputation phase, convex polyhedral beams traced from the location of each sound source are stored in a "beam tree" representing the regions of space reachable by potential sequences of transmissions, diffractions, and specular reflections at surfaces of a 3D polygonal model. Then, during an interactive phase, the precomputed beam tree(s) are used to generate propagation paths from the source(s) to any receiver location at interactive rates. The key features of this beam tracing method are (1) it scales to support large building environments, (2) it models propagation due to edge diffraction, (3) it finds all propagation paths up to a given termination criterion without exhaustive search or risk of under-sampling, and (4) it updates propagation paths at interactive rates. The method has been demonstrated to work effectively in interactive acoustic design and virtual walkthrough applications.

Figure 1: Left, an overview of a test virtual environment, containing 174 sound sources. All vehicles are moving. Mid-left, the magenta dots indicate the locations of the sound sources while the red sphere represents the listener. Notice that the train and the river are extended sources modeled by collections of point sources. Mid-right, ray-paths from the sources to the listener. Paths in red correspond to the perceptually masked sound sources. Right, the blue boxes are clusters of sound sources with the representatives of each cluster in grey. Combination of auditory culling and spatial clustering allows us to render such complex audio-visual scenes in real-time. AbstractWe propose a real-time 3D audio rendering pipeline for complex virtual scenes containing hundreds of moving sound sources. The approach, based on auditory culling and spatial level-of-detail, can handle more than ten times the number of sources commonly available on consumer 3D audio hardware, with minimal decrease in audio quality. The method performs well for both indoor and outdoor environments. It leverages the limited capabilities of audio hardware for many applications, including interactive architectural acoustics simulations and automatic 3D voice management for video games.Our approach dynamically eliminates inaudible sources and groups the remaining audible sources into a budget number of clusters. Each cluster is represented by one impostor sound source, positioned using perceptual criteria. Spatial audio processing is then performed only on the impostor sound sources rather than on every original source thus greatly reducing the computational cost.A pilot validation study shows that degradation in audio quality, as well as localization impairment, are limited and do not seem to vary significantly with the cluster budget. We conclude that our real-time perceptual audio rendering pipeline can generate spatialized audio for complex auditory environments without introducing disturbing changes in the resulting perceived soundfield.

In this paper we present a user-centered design approach to the development of a Virtual Environment (VE), by utilizing an iterative, user-informed process throughout the entire design and development cycle. A preliminary survey was first undertaken with end users, that is, architects, chief engineers, and decision makers of a realworld architectural and urban planning project, followed by a study of the traditional workflow employed. We then determined the elements required to make the VE useful in the real-world setting, choosing appropriate graphical and auditory techniques to develop audiovisual VEs with a high level of realism. Our usercentered design approach guided the development of an appropriate interface and an evaluation methodology to test the overall usability of the system. The VE was evaluated both in the laboratory and, most importantly, in the users' natural work environments. In this study we present the choices we made as part of the design and evaluation methodologies employed, which successfully combined research goals with those of a real-world project.Among other results, this evaluation suggests that involving users and designers from the beginning improves the effectiveness of the VE in the context of the real world urban planning project. Furthermore, it demonstrates that appropriate levels of realism, in particular spatialized 3D sound, high-detail vegetation, and shadows, as well as the presence of rendered crowds, are significant for the design process and for communicating about designs; they enable better appreciation of overall ambience of the VE, perception of space and physical objects, as well as the sense of scale. We believe this study is of interest to VE researchers, designers, and practitioners, as well as professionals interested in using VR in their workplace.

Figure 1: Left: A scene with 1815 mobile sound sources. Audio is rendered in realtime with our progressive lossy processing technique using 15% of the frequency coefficients and with an average of 12 clusters for 3D audio processing. Degradations compared to the reference solution are minimal. Right: a scene with 1004 mobile sound sources, running with 25% of the frequency coefficients and 12 clusters. AbstractDespite recent advances, including sound source clustering and perceptual auditory masking, high quality rendering of complex virtual scenes with thousands of sound sources remains a challenge. Two major bottlenecks appear as the scene complexity increases: the cost of clustering itself, and the cost of pre-mixing source signals within each cluster.In this paper, we first propose an improved hierarchical clustering algorithm that remains efficient for large numbers of sources and clusters while providing progressive refinement capabilities. We then present a lossy pre-mixing method based on a progressive representation of the input audio signals and the perceptual importance of each sound source. Our quality evaluation user tests indicate that the recently introduced audio saliency map is inappropriate for this task. Consequently we propose a "pinnacle", loudness-based metric, which gives the best results for a variety of target computing budgets. We also performed a perceptual pilot study which indicates that in audio-visual environments, it is better to allocate more clusters to visible sound sources. We propose a new clustering metric using this result. As a result of these three solutions, our system can provide high quality rendering of thousands of 3D-sound sources on a "gamer-style" PC.