Lukas Aspöck

Interactive Real-Time Simulation and Auralization for Modifiable Rooms

To study the effects of any changes to a room or setting on the room acoustics, a framework was developed that enables immediate acoustic and visual feedback to the user. This is achieved by running interactive room acoustics simulations and auralizations in real-time. Physically based binaural room impulse responses (BRIRs) are calculated using the image source method and ray tracing and are divided into direct sound, early reflections and late reverberation. Any part of the BRIR is updated as quickly as possible depending on the users interaction with the scene. This includes changes to sources and receivers (positions/orientations/directivities/HRTF), to surface materials and to the room geometry itself. Using streaming low-latency convolution, an immediate feedback is provided to the user. A parallelization concept features multi-threading and networked PC-clusters, so that the workload can be effectively distributed, offering a scalability to simulate small to huge scenes, depending on the available computation power. For convenient scene design and interaction, a plug-in for Trimble SketchUp was developed that enables real-time room acoustics and room acoustics parameter visualization to this easy-to-use CAD modeling tool.

An Extended Binaural Real-Time Auralization System With an Interface to Research Hearing Aids for Experiments on Subjects With Hearing Loss

Theory and implementation of acoustic virtual reality have matured and become a powerful tool for the simulation of entirely controllable virtual acoustic environments. Such virtual acoustic environments are relevant for various types of auditory experiments on subjects with normal hearing, facilitating flexible virtual scene generation and manipulation. When it comes to expanding the investigation group to subjects with hearing loss, choosing a reproduction system which offers a proper integration of hearing aids into the virtual acoustic scene is crucial. Current loudspeaker-based spatial audio reproduction systems rely on different techniques to synthesize a surrounding sound field, providing various possibilities for adaptation and extension to allow applications in the field of hearing aid-related research. Representing one option, the concept and implementation of an extended binaural real-time auralization system is presented here. This system is capable of generating complex virtual acoustic environments, including room acoustic simulations, which are reproduced as combined via loudspeakers and research hearing aids. An objective evaluation covers the investigation of different system components, a simulation benchmark analysis for assessing the processing performance, and end-to-end latency measurements.

Evaluating immersion of spatial audio systems for virtual reality

Multiple aspects influence the quality of experience of different VR presentations. One popular aspect which is usually considered for rating the presentation is the concept of immersion. Its complex nature as well as indistinct definitions make it challenging to use it as an objective measure in scientific experiments. Additionally previous studies revealed contradictory definitions of immersion and its separation from the concept of presence. To investigate immersion, a nomological net was developed which connects various items contributing to immersion. These items were assigned to subcategories and should ideally be well defined and measurable. For each item, multiple questions were formulated. Pre-testing on their linguistic quality and unambiguity was conducted to identify suitable questions for each item. These questions were applied in two listening experiments: A between-group design for the evaluation of the chosen questions and a within-subject design for the evaluation of differences between H...

A hybrid real-time auralization system for binaural reproduction of virtual acoustic environments with simulated room acoustics adapted for hearing aid users

A recently developed binaural real-time reproduction system has been extended with an interface to research hearing aids allowing for the conduction of auditory research on subjects with hearing loss. Simulated hearing aid signals based on measurements of generic hearing aid-related transfer functions are additionally processed on a master hearing aid to emulate conventional hearing aid algorithms and played back through the hearing aid receivers. Designed for subjects with mild to moderate hearing loss, the system also facilitates the use of residual hearing capabilities by simulating an external sound field based on generic head-related transfer functions which is reproduced via loudspeakers and acoustic crosstalk cancellation filters. For increased ecological validity, plausible room acoustics are simulated using adjusted simulation models relying on geometrical acoustics. The proposed system was evaluated objectively on different levels by investigating the listening environment and various system components, running a benchmark analysis on the acoustical simulation and auralization, and measuring the combined system latency.A recently developed binaural real-time reproduction system has been extended with an interface to research hearing aids allowing for the conduction of auditory research on subjects with hearing loss. Simulated hearing aid signals based on measurements of generic hearing aid-related transfer functions are additionally processed on a master hearing aid to emulate conventional hearing aid algorithms and played back through the hearing aid receivers. Designed for subjects with mild to moderate hearing loss, the system also facilitates the use of residual hearing capabilities by simulating an external sound field based on generic head-related transfer functions which is reproduced via loudspeakers and acoustic crosstalk cancellation filters. For increased ecological validity, plausible room acoustics are simulated using adjusted simulation models relying on geometrical acoustics. The proposed system was evaluated objectively on different levels by investigating the listening environment and various system com...

First international round robin on auralization: Results of the acoustical evaluation

The round robin on auralization aimed at a systematic evaluation of room acoustic modeling software by means of comparing simulated and measured impulse responses. While a physical evaluation by means room acoustical parameters and spectro-temporal comparisons is addressed in an accompanying talk, here, we focus on an evaluation of perceptual differences arising in complex room acoustical scenarios. In these cases, a mere physical evaluation might not be able to predict the perceptual impact of the manifold interaction of different sound propagation phenomena in enclosed spaces such as reflection, scattering, diffraction, or modal behavior. For this purpose, dynamic auralizations of binaural room impulse responses that were simulated with different room acoustical modeling softwares were evaluated against their measured counterparts. For this purpose, listening tests were conducted using “plausibility” and “authenticity” as overall quality criteria and the Spatial Audio and Quality Inventory (SAQI) for a ...

Evaluation of higher order sound particle diffraction with measurements around finite sized screens in a semi-anechoic chamber

Noise prediction and room acoustic design rely on simulation methods to model sound propagation. The sound particle simulation method (SPSM), among others, is an increasingly popular choice to do so. In recent years, the combination with the uncertainty based diffraction (UBD), where particles are deflected according to edge bypass distances measured in wavelengths, has helped to overcome typical high frequency limitations. To evaluate SPSM with UBD, 3D simulations are compared to measurements in full scale. As previous attempts to evaluate in real rooms suffered from difficulties to acquire accurate material coefficients, measurements are conducted in a controlled environment. A semi-anechoic chamber allows to examine free-field conditions as well as combinations with floor and wall reflections. This paper focuses on diffraction measurements around one or multiple screens of finite size. This allows the examination of higher order diffraction in combination with reflections. Impulse responses are measure...

First international round robin on auralization: Concept and database

For evaluating the performance of room acoustical simulations or numerical simulations in general, these are usually compared to corresponding measurements as a benchmark. Previous studies indicated that differences may result from neglecting wave effects (scattering, diffraction, attenuation at grazing incidence). However, it also proved to be a challenge to provide a precise representation of the primary and secondary structure (geometry, source and receiver characteristics, absorption and scattering coefficients) of the measured ground truth to be re-modeled in the simulation. The round robin on auralization aimed to overcome such shortcomings by generating a ground truth database of room acoustical environments provided to developers of room simulation software. The database includes a selection of acoustic scenes such as “single reflection,” or “coupled rooms” which isolate single acoustic phenomena, as well as three complex “real-world” environments of different size. Simulated monaural and binaural...

Comparative analysis of absorption coefficients’ effect on room acoustic parameters determined by simulation software

A comparative analysis between different sets of absorption coefficients, found or calculated from a variety of sources and methods, including traditional databases and newer in-situ methods, was carried out. This analysis utilized different architectural acoustic simulation software packages for verification of results and further comparison. Initially, a shoebox model was compared for reference and brief comparison between the software packages was made. Then, the main analysis was conducted using the model of the RWTH Aachen Institute of Technical Acoustics’ Seminar Room. This room was simulated with all the different sets of absorption coefficients through both simulation software packages. The purpose of this analysis was to provide a reference for the variation of room acoustic parameters from the different sources of absorption coefficients.

Determination of boundary conditions for room acoustics simulation by application of inverse calculation models

Simulation models for room acoustics simulation usually promise to deliver precise results for a certain frequency range. However, correct results can only be guaranteed if accurate input parameters are provided. Standardized methods for the determination of boundary conditions, the impedance tube and the reverberation chamber, include measurement uncertainties which might lead to different simulation results. These measurement methods also only capture valid results for special situations, e.g., normal or random wave incidence. This insufficient description of the boundary conditions makes it challenging to validate simulation models by comparing them to measured results. Even for rather simple room acoustic situations, state-of-the-art simulations fail to match measurements using in-situmeasurements or textbook values for the boundary conditions. In geometrical acoustics, these deviations can not only explained by insufficient measurement methods for the input data but also by different handling of refl...

Interactive room auralization of sound sources with exchangeable directivities

Although established measurement methods and simulation models for source directivities are available, there is a lack of tools to directly experience the audible effects of virtual sound sources in different conditions. Only an auralization in connection with psychoacoustic experiments can answer questions regarding the required solution and quality of sound source directivities. This paper presents a real-time simulation engine based on geometrical acoustics which accounts for both source directivities and the room acoustics of the environment. A hybrid simulation model is applied combining an image source model and a ray tracing algorithm to generate a binaural room impulse response, which is then convolved with an anechoic sound file (e.g., of a musical instrument). A convenient user interface is introduced by integrating the simulation engine into the 3D modeling program SketchUp. This makes it possible to easily position virtual sound sources and select various source directivities inside a modifiab...