Search

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.

The ACOUCOU platform is a web-based, interactive, acoustics training platform that includes a set of free educational materials in various technical fields of acoustics. Educational materials are designed to serve as a modern self-development tool for students and engineers, as well as a comprehensive solution for professional education in the work environment. On the other hand, the provided materials of the platform can be a useful tool, supporting teachers, company researchers, and academic lecturers in the process of teaching acoustics. The ACOUCOU platform is a part of a strategic plan for expanding and strengthening acoustic knowledge web-based tools and supporting the development of innovative teaching methods based on attractive and effective delivery of digital content, and best practices at national and international levels. It addresses the challenge of a lack of experts in the acoustics field and the growing needs of the market.

Acta Acustica 6, 28 (2022). doi:10.1051/aacus/2022021, Published by EDP Sciences, Les Ulis

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.

Room acoustical simulations are usually evaluated by comparing them to measurements in corresponding physical environments as a benchmark. However, it proved to be challenging to provide a precise representation of the room geometry, the source and receiver characteristics, and the absorption and scattering coefficients to be re-modeled in the simulation. We aim to overcome these shortcomings by providing a database that can serve as a Benchmark for Room Acoustical Simulations (BRAS) and which is expandable and permanently available to researchers and developers of simulation software. The database includes a selection of reference scenes such as “single reflection”, or “diffraction around an infinite wedge” which isolate specific acoustic phenomena. This article introduces the concept of the BRAS along with the description of the currently contained acoustic scenes and discusses the implication of measurement errors. The acquisition of impulse responses for omnidirectional and binaural receivers, the identification of the boundary conditions, and the data structure is detailed in the database itself. The BRAS is publicly available 1 . The free license under which it is provided allows for future extensions such as additional scenes or improved data due to advanced measurement techniques.

Acta Acustica 5, 26 (2021). doi:10.1051/aacus/2021018, Published by EDP Sciences, Les Ulis

Acta Acustica 5, 19 (2021). doi:10.1051/aacus/2021013, Published by EDP Sciences, Les Ulis

The journal of the Acoustical Society of America 150(3), R5-R6 (2021). doi:10.1121/10.0006097, Published by Acoustical Society of America, Melville, NY

Acta Acustica 5, 18 (2021). doi:10.1051/aacus/2021011, Published by EDP Sciences, Les Ulis

International audience; Reverberation-room measurements of absorption coefficients are subject to high uncertainties and irreproducibility across different laboratories. One reason is the lack of a sufficiently isotropic sound field both in steady-state and during the sound field decay. Recently, two different methods - based on the decomposition of the sound field into plane waves - have been proposed for the estimation and analysis of the sound field isotropy in reverberation rooms [Berzborn, 2018; Gover, 2004; Nolan, 2018]. This study compares the two methods based on numerically calculated plane wave sound fields as well as experimental results obtained from array measurements in a reverberation room in different configurations. The room configurations comprise setups with and without hanging panel diffusers and with and without an absorbing sample on the floor. Both methods are compared regarding their suitability in the analysis of reverberation rooms and the required angular resolution for the plane wave decomposition.

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.

Journal of Advanced Joining Processes 1, 100005 (2020). doi:10.1016/j.jajp.2020.100005, Published by Elsevier, Amsterdam

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.

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.