Real-Time Auralisation of Outdoor Sound Propagation

Abstract

Auralisation describes the process of generating and presenting audible sound using computer programs and audio hardware. Since the result is perceived naturally by the human's auditory system, a demonstration by means of auralisation is easily comprehensible and does neither require background knowledge nor expertise. Producing auralisation under real-time constraints increases the implementation demands significantly. Real-time auralisation is required in applications that respond to user interaction, for example, in interactive Virtual Reality (VR) environments. Dynamically moving sound sources and receivers evoke a change in the perceived sound, and the corresponding result must be provided as quickly as possible. A feeling of immersion can be created if the response time of the system does not exceed perceptual thresholds and thus enables a plausible scene presentation. To achieve this emotional state, real-time auralisation must comply with the expected physical behavior. Because auralisation has gained much attention in room acoustics, the established concepts and approaches are insufficient, if applied to outdoor scenarios. This is due to the fact that simulation principles based on Geometrical Acoustics (GA) can determine specular sound reflection with ease, but only rudimentarily incorporate the contribution of diffracted sound. Nonetheless, the transmission of sound from a source to a receiver in an urban setting contains a significant contribution of reflected and diffracted components. Furthermore, highly dynamic virtual environments are time-variant. Traditional realisations neglect this characteristic, treating an acoustic environment as temporarily static on a frame-by-frame basis. Adaption to dynamic events is implemented by update routines performing sequences of time-invariant simulations, which is contradictory to the highly dynamic nature of outdoor scenarios. This misconception is addressed in this dissertation and an alternative solution is suggested. The realisation of a real-time auralisation application for outdoor environments represents a promising addition to current noise assessment procedures. It also delivers the foundation for auditory modality in VR regarding outdoor scenarios, serving as an audio-video tool for scientific investigations of urban sound environments, accounting for perceptual aspects. der PDs und die Zuordnung individueller Wellenfronten basiert auf einer Winkeldistanzmetrik ("k-means clustering") und die Korrektur der ITD berücksichtigt die Abweichungen im Azimut. Die Machbarkeit des vorgeschlagenen Echtzeit-Auralisierungssystems und die Eignung für die Schallausbreitung im Freien werden in einer interaktiven Applikation demonstriert, die auf VR-Technologien basiert.For the young who are inspiring me, the old who ground me and my dearest who holds everything together.

Directional Spectrum Estimation of Moving Vehicles

“…Virtual acoustic scenarios are simulated applying wave propagation methods to model wave phenomena such as reflection, diffraction and sound absorption [10]. To correctly simulate the sound propagation path between the source and the receiver, two important characteristics of the source must be known: its sound power and its directivity, that is, how the sound energy is spatially emitted.…”

“…Each vehicle is modelled as a "small source with a given directivity pattern", i.e., there is no separation of individual sources, as achieved by acoustic imaging algorithms. This punctual source approach is generally adopted in virtual acoustic simulation tools [8,10]. The point source emits a single audio signal which is modified by the spectral functions according to the direction from the source to the observer.…”