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Beamforming results depend on the spatial resolution of the microphone array used, which may lead to sources close to each other being considered as one. Deconvolution methods that consider all directions simultaneously, such as DAMAS, produce better results in these situations. However, they have a high computational cost, often lack sufficient speed to be used in real-time applications, and have limited accuracy at lower frequencies. This paper introduces a hybrid method to perform deconvolution using a neural network that can improve the speed of deconvolution on high-resolution grids by more than 2 orders of magnitude, while also generating sparser maps without sacrificing accuracy compared to the compressed DAMAS method.

Auralization is a suitable method for the subjective evaluation of environmental noise. Due to its complexity, the plausible and immersive acoustic representation of outdoor scenarios in urban environments is an ongoing field of research. This work presents the design and implementation of a vehicle pass-by noise model with application in a real-time environmental noise auralization. The pass-by noise sources are implemented by procedural audio syntheses of engine and road-tyre noise with according directivities. In an audiovisual demonstration, the resulting source model is auralized considering the sound propagation phenomena in a virtual urban environment using the Virtual Acoustics framework.

Ultrasonic Metal Welding is a type of welding used in the production of electric car batteries. Currently, it suffers from quality fluctuations, and there is a need for online quality control techniques. One technique being investigated involves the measurement of the vibrations of the welding horn using laser vibrometry. However, this comes with two obstacles. First, measurements close to the welding site, which contain the most information, are difficult to do. This is due to the interference of particles ejected during welding, which interfere with the laser beam. Second, it is possible that the use of reflective tape for vibrometry changes the vibrations measured, due to heating of the horn during welding. This work investigates these problems and presents some solutions. The effects of the reflective tape on the measurement is investigated, by measuring the vibrations of the horn during welding and free run, with and without reflective tape, and with and without prior heating of the tape. Furthermore, the interference of ejected particles is minimized using a special experimental setup, and measurements are done without any reflecting tape.

Simulation models based on geometrical acoustics mostly do not immediately deliver a simulated room impulse response, but intermediate results such as an energy histogram or an energy decay curve. At this point, further models are required to generate a room impulse response of the simulated environment, which are essential for the process of auralization. While for various simulated scenarios, the application of a reflection model based on a basic theory is sufficient, detailed comparisons of simulated and measured room impulse responses reveal differences which are attributed to the lack of diffuse reflections in the applied reflection model. These deviations can also substantially affect derived room acoustic parameters. This work presents and explains the shortcomings and discusses potential improvements to be considered in the simulation process.

Analysis of sound source directivity uncertainty for room acoustics simulations and auralizations.

Auralization is a suitable method for subjective noise evaluation of virtual prototypes. A basic requirement is the accurate modelling of the sound sources. This includes a dynamic and parametric description at multiple operating conditions. In the case of wave propagation including flow, such as aircraft or vehicle noise, aeroacoustics or fluid dynamics simulations are practically limited to the acoustic near field due to high computational costs. Especially challenging are simulations of rotating systems, such as fan noise radiation. For better applicability, the proposed method is based on in-situ recordings of flyovers. The processing chain compensates for source position and movement as well as atmospheric and soil damping effects on recorded data. The compensated source signal is decomposed into partial sources in spectro-temporal domain with nonnegative matrix factorization (NMF) and can optionally be enhanced by physically-based source information. The format of the source model obtained is ready to use for dynamic sound synthesis in real-time virtual reality applications.

Analysis of sound source directivity uncertainty for room acoustics simulations and auralizations.

In this paper, the two-zone sound field reproduction problem is investigated with a newly proposed method. The aim of the two-zone reproduction problem is to achieve sound field reproduction in the bright zone while keeping the sound field energy in the dark zone as low as possible. The main difference between the proposed method and the conventional method is that the sound field control in the dark zone is not limited to a small number of measurement points on the region boundary but to measurement points throughout the whole dark zone. For practical reasons, the whole region is discretized into a grid, and the grid selection method is also provided in this paper. Simulations are performed to compare the performances of the proposed and conventional methods with different virtual source directions, and a comparison of the robustness to the regularization parameter shows that the proposed method is less sensitive to the selection of the regularization parameter. Finally, an experiment is performed with a circular loudspeaker array in a real listening room. A quieter dark zone is achieved by the proposed method while keeping the reproduction error in the bright zone close to that of the conventional method, similar to the simulation results. These outcomes verify that the proposed method performs well in both free-field and reverberation environments.

The analysis of the spatio-temporal features of sound fields is of great interest in the field of room acoustics, as they inevitably contribute to a listeners impression of the room. The perceived spaciousness is linked to lateral sound incidence during the early and late part of the impulse response which largely depends on the geometry of the room. In complex geometries, particularly in rooms with reverberation reservoirs or coupled spaces, the reverberation process might show distinct spatio-temporal characteristics. In the present study, we apply the analysis of directional energy decay curves based on the decomposition of the sound field into a plane wave basis, previously proposed for reverberation room characterization, to general purpose performance spaces. A simulation study of a concert hall and two churches is presented uncovering anisotropic sound field decays in two cases and highlighting implications for the resulting temporal evolution of the sound field diffuseness.

Source signal is one of the main input parameters when auralizing moving sound sources in the Virtual Reality (VR) environments. This work utilizes compressive beamforming (CB) as a tool to reconstruct signals from fast moving sources. A pseudorandom microphone array is designed to meet the requirement of using CB and delay and sum beamforming (DSB), thus allowing for the signal reconstruction from the CB output and for the comparison between these two beamforming algorithms. Parameter studies through error analysis are conducted to evaluate how the reconstructed source signal is influenced by parameters, i.e. regularization parameter, window length, signal-to-noise ratio (SNR), basis mismatch and distance between the array and source trajectory. In general, CB outperforms DSB in signal reconstruction in terms of varying every parameter, except for the similar performance with SNR = 30 dB. We used the designed microphone array with both CB and DSB to reconstruct the signal of a known engine noise emitted by a loudspeaker installed on a moving car. The localization results delivered by CB are similar to DSB, which is in line with the simulation results. This behavior can result from potential coherence in the sensing matrix of CB due to similar time-domain transfer functions (TDTFs). However, CB still delivers lower reconstruction errors. Both simulation and measurement results indicate that CB is a viable option to reconstruct the signals of fast moving sound sources.

This paper deals with the question of how specific weather conditions affect the perception of aircraft noise. Auralization is a suitable method by enabling parametrical decompositions of the overall aircraft noise scenario into source and propagation components. Considering influences on the auditory perception, the signal processing chain contains different virtual receivers and post processing using psychoacoustic hearing models. For broad coverage, generic standardized as well as measurement-based atmosphere models with variation of ground impedances such as soil data are evaluated. These variations are given aircraft noise measurement values based on A-weighted sound pressure levels L A and psychoacoustic measures regarding loudness, N, and sharpness, S. The results show an immense influence of weather conditions on A-weighted sound pressure levels and on psychoacoustic perception of aircraft noise, too. The weather-dependent differences of A-weighted sound pressure levels are up to 15 dB A and relative differences regarding loudness of factor 1.6 and sharpness of factor 2.0 occur. The approach can be used to get a better understanding of how the temporal statistics of specific local weather conditions and their perceptual consequences may lead to improved taxation of actual noise events and to an improved basis for long-term averages of aircraft noise effects.

Generating natural embodied conversational agents within virtual spaces crucially depends on speech sounds and their directionality. In this work, we simulated directional filters to not only add directionality, but also directionally adapt each phoneme. We therefore mimic reality where changing mouth shapes have an influence on the directional propagation of sound. We conducted a study (n = 32) evaluating naturalism ratings, preference and distinguishability of omnidirectional speech auralization compared to static and dynamic, phoneme-dependent directivities. The results indicated that participants cannot distinguish dynamic from static directivity. Furthermore, participants' preference ratings aligned with their naturalism ratings. There was no unanimity, however, with regards to which auralization is the most natural.

The aim of this work is to study the sound field distribution in an experimental scale-model of two coupled rooms. An automatic scanning mechanism moves a microphone in small grid steps to measure room impulse responses at each grid point. The measurements cover the entire two-dimensional area of the coupled rooms. Sound energy distributions can be analyzed in the form of animated visual displays, revealing sound propagation across the coupling aperture and inside each room. This paper describes the measurement results, and the analysis method, which offer deep insights into the temporal development of a sound field in coupled spaces.

Virtual environments and their contents are dynamically changing, but also need to respond to the user immediately. While managing a dynamic scene is a common and well-understood problem for visual rendering, additional challenges exist for the high-quality audio rendering of such scenes. Audio rendering differs in a key aspect: Sound waves propagate substantially slower than light. For the acoustics in scenes of large dimensions, it is not sufficient to regard just the state at the current time. The sound propagation times become so significant (perceptible) that the past of the objects matter, making a time history of the scene necessary. Particularly the conjunction of multithreading and low-latency audio processing makes the description of the virtual acoustic scene a problem on its own. This paper presents a novel solution to this acoustic-related problem. We discuss the challenges of realizing a real-time auralization on modern (non-real-time) operating systems and state the main requirements of the data structure. A hierarchical state-based data structure with time history is presented, which not only fulfills the requirements for outdoor auralizations but also has key advantages for indoor simulations—such as room acoustics. A key feature is the integral support of atomic scene modifications, allowing several modifications to be performed at the same time. The presented concept is very modular and beneficial for a wide range of applications.

Using virtual reality (VR) for environmental evaluation is one of the innovations in planning process to support the involvement of local population in decision making. The power of VR in public participation is further enhanced by its application online. However, current online VR applications for public participation is mostly restricted as visualisation tools. Evaluation of the virtual sound environment is rarely supported. This study developed a demonstrator tool of web-based online VR for participatory evaluation of urban sound environment. Piazza Vittoria in Naples, Italy was used as the case site to create the virtual environment. The tool employed affordable visualisation and auralisation for the general public to use online in mainstream web browsers with their own devices. The tool was tested online and the results were analysed to discuss the applicability, potential and challenges of online VR for participatory evaluation of urban sound environment.

Virtual environments should be multimodal and interactive. The technology used for simulation and reproductions must take into consideration the aspect of several sensory inputs in real time and the interaction with the person who is embedded in the virtual environment. In order to achieve a real-time performance, specific runtime conditions must be taken into account in order to stay within acceptable limits for latency and update rates. For the acoustic component of VR, we can use information from psychoacoustics on these limits. In this chapter, the implementation of software and hardware tools is introduced which provide real-time performance and interaction: head tracking and adaptive filtering.

Acoustic waves are fascinating phenomena in gases, liquids or solids with numerous physical and technical aspects. Air is the medium of interest when it comes to audible sound. The gas dynamics of air determine the equations of the sound pressure and other field quantities from which the wave equation can be derived and solved for basic wave types. Properties of the waves such as frequencies and sound levels are associated with the human hearing sensation. The chapter on fundamentals of acoustics deals with the introduction into sound field physics and terminology of acoustics.

In this chapter, the acoustic model of airborne and impact sound transmission and the subsequent auralization technique are generalized towards other applications in acoustics and noise control engineering, particularly to vehicle acoustics. It was shown that the resulting sound pressure signal at the listener’s ears can be constructed by using binaural filters. Sound transmitting elements are accounted for by their transfer function in order to achieve the correct level and colouration. Phase aspects can often be neglected in case of diffuse field conditions in the listener’s environment. Components of early, primary sound, however, must be modelled with their phase or group delay which enhances the presence and immersion and the correct localization. From these components, sources and transfer paths can be constructed and combined into an efficient auralization model.

Auralization of outdoor sound propagation models such as noise mapping is particularly challenging due to wave phenomena which can hardly be solved exactly following the wave equation. Therefore, diffraction and refraction require approximations which are adequate in terms of accuracy but still acceptable as concern computation times. Outdoor scenarios and additionally moving sound sources such as vehicles pose challenges which require special attention. This chapter deals with the question how outdoor sound propagation models and noise mapping models can be enhanced and adapted for auralization.

Computer simulations of acoustic scenes are an important prerequisite for rendering. Technology for 3D sound reproduction, the so-called audio front-end or the acoustic human-machine interface, is an essential component of VR systems, which must be capable of fulfilling high-quality standards concerning the psychoacoustically relevant cues. These cues may differ from one VR application to the next. Some applications require an exact localization, while for others monaural spectral features like reproduction with exact loudness and timbre are more important. In this chapter we focus on electroacoustic technology for surround sound reproduction. It concerns headphone and loudspeaker technology and audio formats which can be used as data interface between systems (Fig. 17.1).

Auralization requires signal processing for merging the sound source signal with the sound propagation filter which was created by measurement or computer simulation. By adding the effects of the environment to the dry sound, we imprint the specific sound character the specific environment into the source. The classical mathematical tool to achieve this is convolution. It can be implemented in brute-force algorithms or in block processing based on FFT algorithms. Furthermore, binaural hearing of human receivers can be implemented along the filtering in a straightforward way. The main concepts are introduced in this chapter.

As previous chapters dealt with virtual environments with sound in free-field and in enclosures (room acoustics, Sect. 11.7), situations with partition walls and complete buildings will be discussed in this chapter. This concerns the field of classical building acoustics as part of architectural acoustics. A typical example dealt with by building acoustics is the problem of sound transmitted into a so-called receiving room from the room next door (source room), for instance, sound from a stereo set that is transmitted into the neighbouring sleeping room. The fundamentals of building acoustics and its auralization are described in this chapter. Another example is impact noise created by walking on the floor in the room above, a typical example of a structure-borne source, which will be treated in Chap. 14. Furthermore, sound generated by building service equipment like heating or air condition systems is of interest. Noise from outside the building, like traffic noise or industrial noise, concerns the sound insulation of facades.

Sound sources are the starting point when it comes to auralization. Their characterization includes the radiation properties such as power and directivity. And the sound signal, the temporal function of the generated sound, is the main input signal for auralization technology. Physical modelling, recording, and sound synthesis can be used for obtaining signals. Databases of frequency-dependent directivities, possibly more aspects with regard to the source mechanisms, their excitation levels and their near-field effects, may be relevant in practical cases, too. In this chapter we consider how sound generation and sound sources can be recorded, modelled and processed and how the main features of sound sources can be implemented in virtual acoustics.

The basics of sound wave radiation and propagation were discussed in the preceeding chapters. Free-field propagation can be studied and simulated with these mathematical models. Numerous problems, however, are related to sound in cavities. This is true for small appliances or vehicles as well as for larger volumes such as living rooms or kitchens, or even large spaces like concert halls and opera houses. In our daily lives, we can analyse by listening whether we are in a room or not, and we can estimate the room volume and amount of absorption from to the auditory impression of the room response. Nevertheless, room acoustical fields are extremely complicated and show a detailed fine structure, depending predominantly on the size of the room. It is therefore appropriate to study at first the physical room acoustic effects based on wave theory. Then, it will be shown that perhaps not all physical details of wave fields are relevant for hearing in rooms. Approximations and considering energy models are also very useful to describe room acoustic effects and for room acoustic modelling. In this chapter, therefore, we extend the theoretical descrption by alternative models of statistical acoustics, diffuse sound fields and reverberation theory.

The straightforward general extension of the propagation and auralization model is discussed now with regard to the excitation of solid structures by forces. The source, therefore, has to be characterized by its force output or by its velocity injected into the medium. With the velocity in the structure being known, transmission and radiation of sound to a receiver can be considered a solved problem. The first example to illustrate this kind of model extension is impact sound in buildings. The basic definitions and methods for prediction and evaluation of impact sound are given in this chapter.

Virtual reality (VR) is a computer-generated environment for interaction in real time. One important feature of VR is the multimodality of the human-computer interface. Most VR systems were initially developed for 3D vision. In order to achieve the presence and immersion of the user, VR is not complete without the acoustic and haptic dimensions (and more). The driving forces for establishing VR applications are task-specific interaction scenarios and their acceptance by the user and user feedback. VR technology includes head-mounted displays, screen displays, and full immersive CAVE syetems, and audio reproduction technology via headphones or surround sound systems. Examples are presented and discussed in this chapter, including references to open-source software for acoustics VR and to benchmarks.

In this chapter we will discuss the fundamental algorithms of geometrical acoustics, their variations of implementation in software and their efficiency. It will be shown that pure specular models (image models) are not capable of simulating room sound fields sufficiently accurate. But combinations of models of image sources and statistical models such as Ray Tracing and radiosity will allow a simulation with acceptable plausibility. Hybrid models which can handle specular and diffuse reflections for the estimation of the late reverberation spectrum are the solution to obtain impulse responses very near to measurement results. For inclusion of wave effects, hybrid models combining numerical methods (FEM, BEM, etc.) with geometrical acoustics have been introduced.

Embodied conversational agents become more and more important in various virtual reality applications, e.g., as peers, trainers or therapists. Besides their appearance and behavior, appropriate speech is required for them to be perceived as human-like and realistic. Additionally to the used voice signal, also its auralization in the immersive virtual environment has to be believable. Therefore, we investigated the effect of adding directivity to the speech sound source. Directivity simulates the orientation dependent auralization with regard to the agent's head orientation. We performed a one-factorial user study with two levels (n=35) to investigate the effect directivity has on the perceived social presence and realism of the agent's voice. Our results do not indicate any significant effects regarding directivity on both variables covered. We account this partly to an overall too low realism of the virtual agent, a not overly social utilized scenario and generally high variance of the examined measures. These results are critically discussed and potential further research questions and study designs are identified.

In the field of automotive engineering there is a lively international competition within each vehicle development sub-discipline. Depending on the vehicle segment, the requirements and customer profile, the development priorities differ for each competitor. In the premium segment, the part NVH, which covers all areas of the acoustic and vibration properties of an automobile has moved closer to the focus of the customers and therefore also the focus of the companies in recent years. Consequently, the effort of the developers is constantly increasing and they take advantage of new, improved analytical methods for practical application. It is the same with the beamforming, the localization and classification of sound sources.

Simulations based on the concepts of geometrical acoustics are today well-established tools for acousticians, being widely used for evaluation of sound quality in rooms and urban spaces. However, although a lot of different models are available and have been evaluated in the past, it is still very important to guarantee the validity and quality of simulated data and reproduced sound. This work presents a comparison between the signal processing strategies in two acoustic simulators based on geometrical models. Obvious expectation was that both simulators would produce the same results when fed by exactly the same input data. However, issues related to model assumptions, propagation methods characteristics and signal processing techniques adopted by each simulator introduce differences which alter the final results, i.e., the simulated acoustic impulse responses. This papers aims to present such deviation and helps to understand the influence of each component over the results. Firstly, both simulators are described in detail, presenting their acoustic models and the signal processing approaches. In addition, an extensive analysis of early reflections is performed, considering pressure levels, reflection order, their arrival time and directional characteristics. Next, simulated energy decay curves, monaural room acoustic parameters and spectra are objectively compared to measured data of a reverberant chamber, in two different conditions. The differences are then pointed out and minimized by unifying the signal processing of both simulators. The results of this comparison reveal that signal processing and inherit method characteristics still have strong influence over the simulated impulse responses, mainly for the late part. Some consequences are energy misbalance between early and late parts of impulse response, leading to differences over the room acoustic parameters, mainly clarity and definition.

This paper describes a novel aircraft noise simulation technique developed at RWTH Aachen University, which makes use of aircraft noise auralization and 3D visualization to make aircraft noise both heard and seen in immersive Virtual Reality (VR) environments. This technique is intended to be used to increase the residents’ acceptance of aircraft noise by presenting noise changes in a more directly relatable form, and also aid in understanding what contributes to the residents’ subjective annoyance via psychoacoustic surveys. This paper describes the technique as well as some of its initial applications. The reasoning behind the development of such a technique is that the issue of aircraft noise experienced by residents in airport vicinities is one of subjective annoyance. Any efforts at noise abatement have been conventionally presented to residents in terms of noise level reductions in conventional metrics such as A-weighted level or equivalent sound level L eq . This conventional approach however proves insufficient in increasing aircraft noise acceptance due to two main reasons – firstly, the residents have only a rudimentary understanding of changes in decibel and secondly, the conventional metrics do not fully capture what the residents actually find annoying i.e. characteristics of aircraft noise they find least acceptable. In order to allow least resistance to air-traffic expansion, the acceptance of aircraft noise has to be increased, for which such a new approach to noise assessment is required.

Radiation patterns of musical instruments are important for the understanding of music perception in concert halls, and may be used to improve the plausibility of virtual acoustic systems. Many attempts have been performed to measure the spatial response of musical instruments using surrounding spherical microphone arrays with a limited number of microphones. This work presents a high-resolution spatial sampling of the radiation pattern of an electrically excited violin, and addresses technical problems that arise due to mechanical reasons of the excitation apparatus using acoustic centering.

In architecture, space is traditionally understood as a cumulus of forms, colors and textures that form a conceived area, or—in other words—architectural space design is mainly achieved by following visual concepts. The human experience of space, however, is multi-modal where light and sound, i.e., eye and ear are the main transducers through which space is perceived. Neglecting aural attributes in room design yields many risks in the overall perception of space, especially when perceptual cues conflict with our expectations in relation to the room’s social and cultural context. State-of-the-art applications in room acoustics prediction and spatial audio reproduction enable the immersive perception and interactive exploration of room designs by establishing a direct link to their acoustical aspects through listening, called auralization. Auralization significantly helps to agree on decisions in room design since standard numerical metrics in room acoustics are often difficult to relate to aural phenomena without serious practice. Therefore, the assessment of space by direct listening enables not only an efficient planning of room acoustics but also adds a new creative dimension to the design. In the course of this article, we will provide some scientific, technical and practical background that takes a faithful auralization of virtual spaces. We will demonstrate that state-of-the-art algorithms and tools already enable a fast and easy design of acoustic spaces by the example of the virtual reconstruction of the old Montreux Casino—an audiovisual installation that was exhibited at the Montreux Jazz Festival 2014 and featured full room acoustics simulation in combination with a 17-channel loudspeaker system for spatial audio reproduction.

Virtual Reality (VR) systems are used in engineering, architecture, design and in applications of biomedical research. The component of acoustics in such VR systems enables the creation of audio-visual stimuli for applications in room acoustics, building acoustics, automotive acoustics, environmental noise control, machinery noise control, and hearing research. The basis is an appropriate acoustic simulation and auralization technique together with signal processing tools. Auralization is based on time-domain modelling of the components of sound source characterization, sound propagation, and on spatial audio technology. Whether the virtual environment is considered sufficiently accurate or not, depends on many perceptual factors, and on the pre-conditioning and immersion of the user in the virtual environment. In this paper the processing steps for creation of Virtual Acoustic Environments and the achievable degree of realism are briefly reviewed. Applications are discussed in examples of room acoustics, archeological acoustics, aircraft noise, and audiology.

In room acoustics analytical formulas and computer simulations can be used to predict the acoustics of spaces, not only in terms of reverberation but other perceptual aspects, too, which are related to the perception of music or speech. In this context the room impulse response is the function of main interest. It can be measured by using sophisticated instrumentation and signal processing, or it can be simulated with computer models. In the process of auralization the data and signal processing enables one to listen into the simulated rooms in order to interpret the sound in the room aurally. In real-time implementation, this is a valuable extension of the technique of virtual reality.

This work presents an analysis of the effect of some uncertainties encountered when measuring absorption or scattering coefficients in the reverberation chamber according to International Organization for Standardization/American Society for Testing and Materials standards. This especially relates to the uncertainty due to spatial fluctuations of the sound field. By analyzing the mathematical definition of the respective coefficient, a relationship between the properties of the chamber and the test specimen and the uncertainty in the measured quantity is determined and analyzed. The validation of the established equations is presented through comparisons with measurement data. This study analytically explains the main sources of error and provides a method to obtain the product of the necessary minimum number of measurement positions and the band center frequency to achieve a given maximum uncertainty in the desired quantity. It is shown that this number depends on the ratio of room volume to sample surface area and the reverberation time of the empty chamber.

Suitable data for spatial wave field analyses in concert halls need to satisfy the sampling theorem and hence requires densely spaced measurement positions over extended regions. The described measurement apparatus is capable of automatically sampling the sound field in auditoria over a surface of 5.30 m × 8.00 m to any appointed resolutions. In addition to discussing design features, a case study based on measured impulse responses is presented. The experimental data allow wave field animations demonstrating how sound propagating at grazing incidence over theater seating is scattered from rows of chairs (seat-dip effect). The visualized data of reflections and scattering from an auditorium's boundaries give insights and opportunities for advanced analyses.