Virtual Acoustics Research Articles

High-Resolution Phase-Based Ranging Using Inverse Fourier Transform in an Iterative Bayesian Approach.

This article proposes an algorithm that determines the distance between two transceivers based on phase information collected in a specific frequency range. Even though we have focused on BLE technology, we do not necessarily adhere strictly to this standard regarding the procedures used to obtain phased samples. We assume that phase samples are given and propose an algorithm using a Bayesian approach to find delays in a multi-path environment. Analyzing these delays allows for determining the distance between both transceivers. We show several examples confirming the high accuracy and resolution of the proposed algorithm. Finally, we conclude with some pros and cons of the proposed solution, suggesting its use in such applications as, for example, virtual acoustics.

Acoustic dynamics in performance halls: Enhancing violin sound quality in the FPSD orchestra room

With an emphasis on improving violin sound quality, this study explores the acoustic dynamics of the FPSD Orchestra Room at Universitas Pendidikan Indonesia. Direct and reflected sound are the two factors that impact the phenomena of interior sound. This research emphasizes the crucial balance between sound absorption and reflection to optimize the acoustic environment and ensure clarity and richness in violin performances. Improving acoustic conditions is vital to increase audience experience and performance quality. The study used a qualitative descriptive research style combining literature review and observations. The research site was the FPSD Orchestra Room, renowned for its historical significance and contribution to music education. The observations revealed significant acoustic obstacles that adversely affected the violin sound's clarity, including excessive reverberation and unequal sound dispersion. The literature review revealed the theoretical underpinnings of sound propagation, reverberation, absorption, reflection, and diffraction. The acoustic environment can be greatly enhanced by introducing sound-absorbing materials to optimize reverberation duration, controlling reflections with diffusers, and utilizing adaptive acoustic systems. Furthermore, combining virtual acoustics technology with digital sound processing systems allows for dynamic control over acoustic parameters, increasing the performance space's adaptability. These improvements provide a customized acoustic environment that supports a variety of musical performances and guarantees the audience a clear, engaging auditory experience. This study emphasizes the significance of fusing cutting-edge technology innovations with conventional acoustic design concepts to attain optimal sound quality in performance halls. Innovation and research must never stop to improve these acoustic settings even further.

A real-world Lexicon 960L reverberation chamber: Simulating a hardware reverberation unit in virtual acoustics

The second generation of the Virtual Acoustic Technology (VAT) Laboratory at McGill University features a new real-time auralizer with a feedback canceller developed by CCRMA at Stanford University, allowing for the simulation of virtual acoustic environments with exceptionally high gain. This study is part of an ongoing research effort focused on integrating algorithmic reverberation tools designed for audio post-production into virtual acoustics at McGill University’s VATLab. Previous work has been done using impulse responses (IRs) captured from various acoustic spaces. In contrast, this study focuses on using IRs captured from the legendary Lexicon 960L hardware reverberation unit and using them in the VATLab for recording sessions with musicians. Various 5.1 multichannel presets have been captured as IRs and 3 groups of related 5 channel IRs have been loaded into the existing 15 speaker system of VATLab to simulate a real world, physical Lexicon 960L “environment” through virtual acoustics. Objective measurements following the ISO 3382-1 and 3382-2 standards in the VATLab have been performed to measure the effect of the physical room and analyze the effects of changing different algorithmic reverb parameters such as Diffusion, Early Level Master Control, Early Rolloff, Early or Reflection Delays on the simulated acoustical environments.

Virtual acoustics in distributed performance over a closed audio network

We explore an application of active acoustics used to produce a shared virtual environment for live musical performance. As part of a concert given in the Immersive Media Lab at McGill University, musicians and audience members were located in adjacent but acoustically isolated spaces on the same digital audio network. With computer generated effects and live instruments, the concert consisted of electroacoustic performances that utilized dynamic virtual environments produced by our Virtual Acoustic Technology (VAT) system as an improvisatory partner and a mixing device to blend the diffusion of electronic and acoustic musical sources. The performance, including its evolving virtual environment, was captured using spatial microphone techniques and distributed in real-time to the audience over an immersive loudspeaker system in an adjacent control room. Audience members were given the opportunity to visit the musicians’ performance space in order to compare the reproduction to the original environment. Overall, the blending of computer-generated and acoustic sources created a specific use case for virtual acoustics, while the immersive capture and distribution method examined an avenue for producing a real-time shared experience. Future work in this area includes audio networks with multiple virtual acoustic environments and distributions.

Enhancement of virtual acoustics rendering using boundary mounted dipole loudspeakers

The Immersive Media Lab at McGill University hosts a Virtual Acoustics Technology (VAT) system incorporating a suspended array of omnidirectional loudspeakers. Using a convolution reverb engine, acoustic simulations of real spaces can be realized via a catalog of Room Impulse Response measurements. Reflected sound in the room helps to disguise the location of the sound emitters rendering virtual acoustics. One limitation of the system, however, is the interference between the lab’s natural acoustics and the virtual environment generated by the VAT system. The improvement under consideration is to enhance diffusion along the walls of the lab, in order to mask the acoustical characteristics related to the physical dimensions of the room. Dipole loudspeakers are installed on the room boundaries and used to scatter reflections and reverberation along the wall surfaces enlarging the effective radiation surface of the walls. The scattered energy may mask specular reflections and reduce localization of the virtual acoustic sources. Investigations compare the result of scattering reflected sound vertically as opposed to horizontally across the boundaries. Measurements illustrate the effect of the dipole loudspeaker system when used on its own as well as working in conjunction with the existing omnidirectional loudspeaker array.

Simulation of acoustical parameters of churches in a virtual acoustics laboratory

Current ISO standards for acoustical assessment limit the use of traditional mono-dimensional microphones for measuring equipment. However, microphone arrays offer more accurate spatial information compared to traditional microphones. This presents an opportunity to enhance research on architectural acoustics and preserve the acoustics of cultural heritage more effectively. Furthermore, modern recording studios equipped with virtual acoustics systems allow for the integration of spatial room impulse responses. This enables real-time auralization in controlled environments and enhances the overall immersive audio experience for users and musicians. This paper analyzes the main acoustical parameters obtained from spatial impulse responses captured in churches using various ambisonic microphones and inserted into a controlled, interactive, and immersive virtual acoustics system. The captured spatial acoustic measurements are then reproduced and evaluated in a virtual acoustics laboratory to identify any discrepancies between real and virtual spaces.

Musician-led performance perspectives in virtual acoustics

Musical performance is a complex task that involves juggling performance techniques, creative expression and auditory feedback, all of which in turn affect a musician’s perception of their acoustic environment. Synthesized here are several recent studies conducted at McGill University in variable acoustic spaces: the Multimedia Room (with a Meyer Constellation system) and the Immersive Media Lab (utilizing a proprietary Virtual Acoustics Technology system). In studying the perception of room response, variable acoustic environments allow researchers to physically and/or virtually change the character of a space around a musician without the need for a physical venue relocation. These experiments explore different methodologies and approaches to studying the perception of room acoustic response of various vocalists and instrumentalists who completed both solo and group performance tasks. After contextualizing these studies with previous work done in this area, lessons recently learned point towards new methodologies for musician-led perspectives on room perception.

Urban background sound recordings for virtual acoustics under various weather conditions

One of the major challenges in the auralization of complex urban simulations is the presence of ambience, for example background sounds. Omitting them can result in a sterile and implausible impression. In this work we present a dataset of spatially recorded ambient sounds with metadata on meteorological and acoustical parameters. The recordings are ready to be admixed with simulated soundscapes corresponding to various weather conditions. In particular, 28 soundscapes have been recorded at the IHTApark (green space next to the Institute for Hearing Technology and Acoustics) in Aachen (Germany) in winter and spring. They have been segmented into 30-s auralizable snippets. Moreover, the database contains a statistical and psychoacoustical evaluation of the recordings.

Directional reverberation time and the image source method for rectangular parallelepipedal rooms.

The image source (IS) method is a commonly used geometrical acoustics simulation technique in room and virtual acoustics. In particular, it has been used in the analysis of room reverberation under different choices of geometry and wall conditions. Under a simple rectangular parallelepipedal geometry, reverberation time is known to be dependent on the direction of arrival of reflections relative to the room axes. In this article, a closed-form expression for the directional energy decay and reverberation time is derived, which is valid in the late response, and may be used in the case of either angle-independent or angle-dependent reflection. The expression reduces to an easily evaluated formula in the case of an omnidirectional energy decay curve (EDC). Various numerical results are presented, including the validation of the closed-form expression against EDCs and late reverberation times drawn directly from the IS method.

The Impact of Hearing Aids on Listening Effort and Listening-Related Fatigue - Investigations in a Virtual Realistic Listening Environment.

Participation in complex listening situations such as group conversations in noisy environments sets high demands on the auditory system and on cognitive processing. Reports of hearing-impaired people indicate that strenuous listening situations occurring throughout the day lead to feelings of fatigue at the end of the day. The aim of the present study was to develop a suitable test sequence to evoke and measure listening effort (LE) and listening-related fatigue (LRF), and, to evaluate the influence of hearing aid use on both dimensions in mild to moderately hearing-impaired participants. The chosen approach aims to reconstruct a representative acoustic day (Time Compressed Acoustic Day [TCAD]) by means of an eight-part hearing-test sequence with a total duration of approximately 2½ h. For this purpose, the hearing test sequence combined four different listening tasks with five different acoustic scenarios and was presented to the 20 test subjects using virtual acoustics in an open field measurement in aided and unaided conditions. Besides subjective ratings of LE and LRF, behavioral measures (response accuracy, reaction times), and an attention test (d2-R) were performed prior to and after the TCAD. Furthermore, stress hormones were evaluated by taking salivary samples. Subjective ratings of LRF increased throughout the test sequence. This effect was observed to be higher when testing unaided. In three of the eight listening tests, the aided condition led to significantly faster reaction times/response accuracies than in the unaided condition. In the d2-R test, an interaction in processing speed between time (pre- vs. post-TCAD) and provision (unaided vs. aided) was found suggesting an influence of hearing aid provision on LRF. A comparison of the averaged subjective ratings at the beginning and end of the TCAD shows a significant increase in LRF for both conditions. At the end of the TCAD, subjective fatigue was significantly lower when wearing hearing aids. The analysis of stress hormones did not reveal significant effects.

Benefit of Hearing-Aid Amplification and Signal Enhancement for Speech Reception in Complex Listening Situations.

A major goal of hearing-device provision is to improve communication in daily life. However, there is still a large gap between the user's daily-life aided listening experience and hearing-aid benefit as assessed with established speech reception measurements in the laboratory and clinical practice. For a more realistic assessment, hearing-aid provision needs to be tested in suitable acoustic environments. In this study, using virtual acoustics, we developed complex acoustic scenarios to measure speech-intelligibility and listening-effort benefit obtained from hearing-aid amplification and signal enhancement strategies. Measurements were conducted using the participants' own devices and a research hearing aid, the Portable Hearing Laboratory (PHL). On the PHL, in addition to amplification, a monaural and a binaural directional filter, as well as a spectral filter were employed. We assessed the benefit from different signal enhancement strategies at the group and the individual level. At the group level, signal enhancement including directional filtering provided a higher hearing-aid benefit in challenging acoustic scenarios in terms of speech intelligibility compared to amplification alone or combined with spectral filtering. However, no difference between monaural and binaural signal enhancement occurred. On an individual level, we found large differences in hearing-aid benefit between participants. While some benefitted from signal-enhancement algorithms, others benefitted from amplification alone, but additional signal enhancement had a detrimental effect. This shows the importance of an individual selection of signal enhancement strategies as a part of the hearing-aid fitting process.

Auditory Spatial Bisection of Blind and Normally Sighted Individuals in Free Field and Virtual Acoustics.

Sound localization is an important ability in everyday life. This study investigates the influence of vision and presentation mode on auditory spatial bisection performance. Subjects were asked to identify the smaller perceived distance between three consecutive stimuli that were either presented via loudspeakers (free field) or via headphones after convolution with generic head-related impulse responses (binaural reproduction). Thirteen azimuthal sound incidence angles on a circular arc segment of ±24° at a radius of 3 m were included in three regions of space (front, rear, and laterally left). Twenty normally sighted (measured both sighted and blindfolded) and eight blind persons participated. Results showed no significant differences with respect to visual condition, but strong effects of sound direction and presentation mode. Psychometric functions were steepest in frontal space and indicated median spatial bisection thresholds of 11°-14°. Thresholds increased significantly in rear (11°-17°) and laterally left (20°-28°) space in free field. Individual pinna and torso cues, as available only in free field presentation, improved the performance of all participants compared to binaural reproduction. Especially in rear space, auditory spatial bisection thresholds were three to four times higher (i.e., poorer) using binaural reproduction than in free field. The results underline the importance of individual auditory spatial cues for spatial bisection, irrespective of access to vision, which indicates that vision may not be strictly necessary to calibrate allocentric spatial hearing.

The Right-Ear Advantage in Static and Dynamic Cocktail-Party Situations.

When presenting two competing speech stimuli, one to each ear, a right-ear advantage (REA) can often be observed, reflected in better speech recognition compared to the left ear. Considering the left-hemispheric dominance for language, the REA has been explained by superior contralateral pathways (structural models) and language-induced shifts of attention to the right (attentional models). There is some evidence that the REA becomes more pronounced, as cognitive load increases. Hence, it is interesting to investigate the REA in static (constant target talker) and dynamic (target changing pseudo-randomly) cocktail-party situations, as the latter is associated with a higher cognitive load than the former. Furthermore, previous research suggests an increasing REA, when listening becomes more perceptually challenging. The present study examined the REA by using virtual acoustics to simulate static and dynamic cocktail-party situations, with three spatially separated talkers uttering concurrent matrix sentences. Sentences were presented at low sound pressure levels or processed with a noise vocoder to increase perceptual load. Sixteen young normal-hearing adults participated in the study. The REA was assessed by means of word recognition scores and a detailed error analysis. Word recognition revealed a greater REA for the dynamic than for the static situations, compatible with the view that an increase in cognitive load results in a heightened REA. Also, the REA depended on the type of perceptual load, as indicated by a higher REA associated with vocoded compared to low-level stimuli. The results of the error analysis support both structural and attentional models of the REA.

Listening in Sacred Spaces: The Sanctuary of Poseidonia and Selinunte’s Main Urban Sanctuary

Abstract The aim of this work is to analyse recent studies which have raised new hypotheses concerning aural architecture as an emerging trend in humanities research, with a particular focus on the intersection of sacred space, rituals, and sound in the past. These studies have highlighted how sacred buildings not only defined a sacred place as a physical and symbolic expression of a specific form of worship but also established the setting for performative and multisensorial ceremonies in which music, dance, and other sonic events played an important role. In this contribution, we investigate studies on aural architecture to explore if the location of sacred spaces indicates whether ancient people reacted to ritual and musical developments by modifying sanctuaries or by designing and constructing new buildings and spaces for performances. In addition, this article explores studies on aural architecture to obtain an overview of how specific sonic features could have influenced the soundscape of sacred spaces, which consisted not only of songs, music, prayers, recitations and religious sonic and vocal utterances but also of natural elements, such as animals, water, and wind. This overview also takes into consideration how digital technologies and virtual acoustics can help shape our understanding of the architecture-sound nexus.

Complex Source Distributions in Wave-based Virtual Acoustics

In the typical scenario in time-domain wave-based acoustics, the solution to the acoustic wave equation is approximated over a three-dimensional volumetric grid using a time stepping method. In the setting of very large simulations, the grid is normally assumed to be regular (e.g. Cartesian) so that massive parallelism may be exploited. One difficulty has been in representing source distributions that do not conform neatly to a regular grid. Using a Fourier-based optimisation procedure in the wave vector domain, it is possible to represent arbitrary source distributions in a flexible way over a pre-defined collection of grid points. Such a methodology is independent of the particular choice of simulation method and depends only on the regularity of the grid. In this paper, approximations to various simple distributions, including the line source and piston, are examined, with regard to accuracy, rotation of the distribution relative to the grid, and the size of the point cloud used to represent the source. Numerical results are presented.

A real-time auralization framework for scientific experiments

The software Virtual Acoustics (VA) is an open-source auralization framework developed at the Institute for Hearing Technology and Acoustics, RWTH Aachen University, Germany. Using physics-based models for source emission and sound propagation, it allows plausible rendering of virtual scenes based on purely synthetic data. Its modular design provides a variety of rendering modules using different assumptions for the sound propagation. This allows the rendering of various indoor and outdoor scenarios with adjustable degree of complexity. Based on a similarly modular concept, VA allows a flexible way of reproducing the sound via headphones or loudspeaker arrays. For this purpose, the signals can be spatialized using binaural synthesis, higher-order ambisonics or VBAP. The respective scenarios, including source and receiver movement, can be controlled using the C + +, C#, Matlab, Python programming languages. Additionally, there are interfaces for the Unreal and Unity game engines allowing the combination with sophisticated visual cues, e.g., using HMDs. The software’s flexible structure and configuration possibilities enable the controlled application in listening experiments while providing an adequate level of plausibility. This work discusses the options as well as the limitations of the software and presents application examples in scientific experiments.

Head-related transfer functions upsampling with physics-informed spherical convolutional neural network

Head-related transfer functions (HRTFs) play a crucial role in virtual acoustics and spatial audio applications. However, obtaining personalized, high-resolution HRTFs remains challenging due to the time-consuming and expensive measurements. Recently, deep learning-based methods have shown promise in predicting high-resolution HRTFs from sparse measurements. Nevertheless, most of these methods often treat HRTF upsampling as an image super-resolution task, which overlooks critical spatial information and acoustic principles, leading to overfitting on datasets. This paper proposes a physics-informed spherical convolutional neural network for HRTF upsampling. First, spherical convolutional layers are used to capture spatial features on the sphere, allowing efficient handling of spherical sampled HRTF data. Second, in the upsampling process, the proposed method incorporates the Helmholtz equation as a constraint, adhering tothe physics of the acoustic system. This method ensures the generation of physically feasible HRTF interpolations, thus promoting better generalization.

Filter-based solutions for finite and infinite edge diffraction

Sound diffraction occurs at (building) corners, objects and openings, prominently affecting occluded and reflected sounds. Here, a physically-based, parametric filter model for diffraction at arbitrary wedges is presented. The model connects existing high-frequency asymptotic and exact solutions in geometrical acoustics using up to four half-order low-pass filters. Compact expressions for the transfer function and impulse response of the singly diffracted field are derived, with errors below 0.1 dB. A filter modification is suggested to account for the exact solution at low frequencies. The filter solution is further simplified to approximate the spectral effects of diffraction from finite wedges and objects composed thereof, referred to as universal diffraction filter approximation (UDFA). A computationally highly-efficient recursive filter implementation is presented and it is demonstrated that diffraction from flat finite objects like plates or apertures can be closely approximated. To account for effects of higher-order diffraction at the object, a heuristic filter extension is suggested. The presented filter-based diffraction solution is suited for the prediction and simulation of sound propagation including non-specular reflections in architectural acoustics. For virtual acoustics, UDFA provides an efficient and accurate approximation of edge diffraction to account for perceptually relevant frequency-dependent attenuation, extendable to arbitrary objects.

Acoustically-mediated orientation and navigation in rooms

While the visual system provides the dominating sensory input in sighted humans for awareness, orientation, and navigation, in low-light conditions, smoke, or in visually-impaired and blind individuals, auditory perception becomes important. Acoustic information about the environment includes sounds radiated from sources, as well as reflections and reverberation in enclosed spaces in response to either external sound sources or self-produced sounds (e.g., mouth clicks), referred to as echolocation. Here, we investigated orientation and navigation in typical corridors based on acoustic cues only, using sighted humans without training and real-time virtual acoustics. Virtual sound sources and echo-location with predefined sounds as well as own vocalizations were used with the goal to identify suitable techniques for an acoustically augmented reality (AAR) based mobility aid. A hand-held acoustic pointer, rendering virtual sound sources at the closest wall in the pointing direction was best suited for orientation and navigation. For identification of the room shape, a performance similar to that obtained with a reference (visual) laser pointer could be achieved with the acoustic pointer in specific conditions. In addition to the above acoustic pointer, an AAR-based echolocation pointer with highly directed sound radiation, as achievable in the ultrasonic range, was additionally suggested.

A Review of Finite Element Methods for Room Acoustics

Accurate predictions of the wave-dominated region of an acoustic field in a room can be generated using wave-based computational methods. One such method is the finite element method (FEM). With presently available computing power and advanced numerical techniques, it is possible to obtain FEM predictions of sound fields in rooms with complicated geometries and complex boundary conditions in realistic time frames. The FEM has been continuously developed since its inception and attempts to provide solutions in real time using finite element-based methods are beginning to appear in the literature; these developments are especially interesting for auralization and virtual acoustics applications. To support these efforts, and provide a resource for neophytes, the use of the FEM for room acoustics is reviewed in this article. A history is presented alongside examples of the method’s derivation, implementation, and solutions. The current challenges and state-of-the-art are also presented, and it is found that the most recent contributions to the field make use of one or a mixture of the following: the finite element-based discontinuous Galerkin method, extended reaction boundary conditions written in the frequency domain but solved in the time domain, and the solution of large-scale models using parallel processing and graphics processing units.