Michael Vorlaender

Effects of practical loudspeaker characteristics on virtual acoustic imaging systems

Loudspeakers used in virtual acoustic imaging systems are usually considered as monopoles in the models; however, it is only an approximation at low frequency range, and practical loudspeaker boxes behave complex directivity in mid to high frequency range and almost only radiate in the front direction above a certain frequency. Some studies have taken into account of the frequency response characteristics of the loudspeakers in virtual acoustic imaging systems, and others have considered their directivity characteristics separately. This paper presents a complete model of a virtual acoustics imaging system which takes account of both the temporal and spatial characteristics of the sound sources, and the effects of practical loudspeaker characteristics on virtual acoustic imaging systems are studied.

Evaluation and improvement of a model to predict the measurement uncertainty due to the directivity of room acoustical sound sources

With the aim to reduce the necessary efforts to empirically determine the uncertainty in room acoustical measurements, in previous work, a model was developed that can predict the uncertainty a directivity of a sound source introduces to a measurement. As part of the validation extensive series of scale measurements have been conducted. In this contribution, the predicted uncertainty based on simulations and the empiric data is compared to each other. The results were used to improve the model. Concluding it will be discussed whether the model is suitable for a reasonable measurement uncertainty discussion.

A revised scale model reverberation chamber for measurements of scattering coefficients.

For measurements of random‐incidence scattering coefficients according to ISO 17497‐1, scale models have proven to yield results with reasonable time and effort. Especially, handling the samples becomes much easier so that several measurements, which may be difficult or even unfeasible in a full‐scale reverberation chamber, turn out to be possible. Despite these advantages, using a scale model environment poses other difficulties that are related to the extended frequency range. In order to achieve a better repeatability and stability of the measurements, a revised scale model room is proposed. As a further development from the ordinary scale model rooms, the turntable can now be lowered so that the rotating base plate is mounted flush with the floor. The previously used hanging panels have been replaced with wall‐panel diffusers. Furthermore, the chamber includes temperature and humidity sensors to enable correction for air absorption. Measurements in the new model room are performed to evaluate the quality of the results compared with reference data from calculation and the repeatability of the measurements. Results will be compared for different room setups.

The next generation of artificial heads

Standardised artificial heads are vital means when it comes to describing the binaural transmission from the sound field into the ear canal or rather the eardrum. In recent years numerous fields of application were created ranging from room acoustics, to product sound design or telecommunications, all based on the well‐known KEMAR standard IEC TR 959. In the meantime, however, it has become a well‐known fact, that a) specific artificial heads with natural heads or replicas in hearing experiments are superior to standard artificial heads as far as the quality of spatial hearing is concerned and that b) the standardised heads do not comply with the dimensions of an average population (the standard heads are too small). In this contribution first of all todays situation will be assessed and then a possible way will be outlined that could lead to a new future artificial head standard. This includes an adequate match with adult population for various continents, and also new approaches such as children‐size a...

Real‐time audio rendering system for virtual reality

Systems of virtual acoustics are more and more coming into the focus of research and application. Creating a virtual sound scene with spatially distributed sources requires a technique for adding spatial cues to audio signals and an appropriate reproduction. A real‐time audio rendering system is introduced that combines room acoustics, dynamic crosstalk cancellation, and multitrack binaural synthesis for virtual acoustical imaging. The room acoustics component takes into account the full up‐to‐date algorithmic approach of specular reflections and scattering, but with real‐time processing. The real‐time performance of the software was reached by introduction of a flexible framework for the interactive auralisation of virtual environments. The concept of scene graphs for the efficient and flexible linkage of autonomous‐operating subscenes by means of so‐called portals has been incorporated into the existing framework, combined with an underlying BSP‐tree structure for processing geometry issues very fast. U...

Analysis of sound field isotropy based on directional energy decay curves

The analysis of the diffuseness of sound fields is of great interest in room acoustic applications ranging from the analysis of concert venues to reverberation room design and calibration. However, a standardized robust diffuseness estimation method is currently lacking. The fundamental definition of the diffuse sound field is that it is isotropic—requiring the sound field to be composed of infinitely many sound waves from uncorrelated sources with directions of arrival uniformly distributed over a sphere. Due to their symmetry, spherical microphone arrays are especially favorable for the analysis of the isotropy requirement. In this work, we propose the directional energy decay curve which we calculate from a directional room impulse response captured with a spherical microphone array. Further, we show how the analysis of the spatial variations of the directional energy decay curve enables examining the isotropy of sound fields in rooms. Finally, we present a simulation study of multiple room configurations with varying degrees of sound field diffuseness.The analysis of the diffuseness of sound fields is of great interest in room acoustic applications ranging from the analysis of concert venues to reverberation room design and calibration. However, a standardized robust diffuseness estimation method is currently lacking. The fundamental definition of the diffuse sound field is that it is isotropic—requiring the sound field to be composed of infinitely many sound waves from uncorrelated sources with directions of arrival uniformly distributed over a sphere. Due to their symmetry, spherical microphone arrays are especially favorable for the analysis of the isotropy requirement. In this work, we propose the directional energy decay curve which we calculate from a directional room impulse response captured with a spherical microphone array. Further, we show how the analysis of the spatial variations of the directional energy decay curve enables examining the isotropy of sound fields in rooms. Finally, we present a simulation study of multiple room configurati...

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 ...

Simulation of acoustic environments—Part 2: Can we trust the computer?

The lessons learned from the “round robins” are that the main bottlenecks in room acoustic computer simulations are lack of data of 3D characterization of sound sources and material parameters, and interfaces to spatial audio technology. This presentation focuses on sources of uncertainties in such computer models and on the challenges in solving indoor acoustic problems. Also, a new initiative towards a fourth “round robin” on auralization is presented, which will be further elaborated in other papers of the special session.