Realistic sound propagation is important for immersive game audio, yet its implementation remains a balance between physics-based accuracy and creative design. This paper presents a survey on physics-based techniques for sound propagation rendering in video games. It explores the perspectives of professional sound designers working in the video games industry, examining their approaches and prioritization in implementation. The key findings reveal a complex relationship between physicsbased calculation and creative design preferences, highlighting a significant gap between academic theory and practical solution design. The study offers a practical discussion and insights for implementing sound propagation effects in industry projects.

Viking VR is a Virtual Reality exhibit through which viewers can experience the sights and sounds of a 9th Century Viking encampment. Created as part of a major museum exhibition, the experience was developed by an interdisciplinary team consisting of artists, archaeologists, curators and researchers. In this paper, approaches to the design of authentic, informative and compelling VR experiences for Cultural Heritage contexts are discussed. We also explore issues surrounding interaction design for the long-term deployment of VR experiences in museums and discuss the challenges of VR authoring workflows for interdisciplinary teams.

Articulatory speech synthesis has the potential to offer more natural sounding synthetic speech than established concatenative or parametric synthesis methods. Time-domain acoustic models are particularly suited to the dynamic nature of the speech signal, and recent work has demonstrated the potential of dynamic vocal tract models that accurately reproduce the vocal tract geometry. This paper presents a dynamic 3D digital waveguide mesh (DWM) vocal tract model, capable of movement to produce diphthongs. The technique is compared to existing dynamic 2D and static 3D DWM models, for both monophthongs and diphthongs. The results indicate that the proposed model provides improved formant accuracy over existing DWM vocal tract models. Furthermore, the computational requirements of the proposed method are significantly lower than those of comparable dynamic simulation techniques. This paper represents another step toward a fully functional articulatory vocal tract model which will lead to more natural speech synthesis systems for use across society.

Following recent advances in direct modeling of the speech waveform using a deep neural network, we propose a novel method that directly estimates a physical model of the vocal tract from the speech waveform, rather than magnetic resonance imaging data. This provides a clear relationship between the model and the size and shape of the vocal tract, offering considerable flexibility in terms of speech characteristics such as age and gender. Initial tests indicate that despite a highly simplified physical model, intelligible synthesized speech is obtained. This illustrates the potential of the combined technique for the control of physical models in general, and hence the generation of more natural-sounding synthetic speech.

Computer games and virtual reality require digital reverberation algorithms, which can simulate a broad range of acoustic spaces, including locations in the open air. Additionally, the detailed simulation of environmental sound is an area of significant interest due to the propagation of noise pollution over distances and its related impact on well-being, particularly in urban spaces. This paper introduces the waveguide web digital reverberator design for modeling the acoustics of sparsely reflecting outdoor environments; a design that is, in part, an extension of the scattering delay network reverberator. The design of the algorithm is based on a set of digital waveguides connected by scattering junctions at nodes that represent the reflection points of the environment under study. The structure of the proposed reverberator allows for accurate reproduction of reflections between discrete reflection points. Approximation errors are caused when the assumption of point-like nodes does not hold true. Three example cases are presented comparing waveguide web simulated impulse responses for a traditional shoebox room, a forest scenario, and an urban courtyard, with impulse responses created using other simulation methods or from real-world measurements. The waveguide web algorithm can better enable the acoustic simulation of outdoor spaces and so contribute toward sound design for virtual reality applications, gaming, and auralization, with a particular focus on acoustic design for the urban environment.

The Finite Difference Time Domain method is gaining popularity as a means to simulate and solve room acoustical problems. In this paper, a new set of stencils is defined that approximate the wave equation with a high degree of accuracy and lower dispersion error. Compared to the previously presented optimal scheme, the Interpolated Wideband scheme, our schemes are computationally less demanding and more practical to implement. They use at least 8 times less memory for the same audio rate and are an order of magnitude faster, although the former has a higher valid bandwidth. Despite their larger computational expense per node update, it is shown that our schemes on the whole use less memory and computation time than the Standard Rectilinear stencil, particularly when GPU implementations are employed. Lastly, a new way of visualizing and comparing valid bandwidth is recommended.

The digital waveguide mesh has been shown to be capable of reproducing the acoustic impulse response of cylindrical vocal tract analogs. This study extends the same methodology to three-dimensional simulation of the acoustic response of graphical models of the vocal tract obtained from magnetic resonance imaging for a group of trained subjects. By such simulation of the vocal tract transfer function and convolution with an appropriate source waveform, basic phonemes are resynthesized and compared with benchmark audio recordings. The technologies and techniques used for simulation are described, alongside the protocol for image capture and the process for collection of benchmark audio. The results of simulation and acoustic recording are then evaluated and compared. The value of three-dimensional simulation in comparison to existing lower-dimensionality equivalents is assessed. It is found that while three-dimensional simulation provides a strong representation of the low frequency vocal tract transfer function, at higher frequencies its performance becomes geometry-dependent. MRI imaging and benchmark audio is provided for future studies and to permit comparison with comparable means of acoustic simulation.

Synthesizing the room impulse response (RIR) of an arbitrary enclosure may be performed using a number of alternative acoustic modeling methods, each with their own particular advantages and limitations. This article is concerned with obtaining a hybrid RIR derived from both wave and geometric-acoustics based methods, optimized for use across different regions of time or frequency. Consideration is given to how such RIRs can be matched across modeling domains in terms of both amplitude and boundary behavior and the approach is verified using a number of standardised case studies.

3D time-domain acoustic modeling techniques have the potential to produce more accurate simulation of the vocal tract than previously implemented 1D or 2D solutions, although the variability of human voice renders it a problematic benchmark for validation of its resynthesis. This study uses acoustic measurement of acrylic cylindrical vocal tract models derived from X-Ray data to assess the validity of comparable 3D digital waveguide mesh simulations. It is found that for more simple structures the 3D digital waveguide mesh is able to reproduce the acoustic behavior up to 10 kHz with only slight errors in resonant frequencies. As the simulated structures become more geometrically complex, this shifting becomes more severe.

A single room impulse response can reveal information about the acoustics of a given space in both objective, and, when used for auralization, subjective terms. However, for additional spatial information, or more accurate and perceptually convincing auralization, multiple impulse responses are needed. Higher order Ambisonics is a robust means of capturing the spatial qualities of an acoustic space over multiple channels for decoding and rendering over many possible speaker layouts. A method for obtaining$N$th-order Ambisonic impulse responses from a room acoustic model, based on lower orders using differential microphone techniques is presented. This is tested using a third-order encoding of a 2-D finite difference time domain room acoustic simulation based on multiple circular arrays of receivers. Accurate channel directional profiles are obtained and results are verified in a series of listening tests comparing the localization of a sound source placed within the given simulation to the same source encoded directly. This generic encoding scheme can be applied to any room acoustic simulation technique where it is possible to obtain impulse responses across multiple receiver positions. Although the proposed method encompasses horizontal encoding only, it can also be applied directly in 3-D simulations where height information is not required in the final auralization.

In this paper, a method for modeling diffusive boundaries in finite-difference time-domain (FDTD) room acoustics simulations with the use of impedance filters is presented. The proposed technique is based on the concept of phase grating diffusers, and realized by designing boundary impedance filters from normal-incidence reflection filters with added delay. These added delays, that correspond to the diffuser well depths, are varied across the boundary surface, and implemented using Thiran allpass filters. The proposed method for simulating sound scattering is suitable for modeling high frequency diffusion caused by small variations in surface roughness and, more generally, diffusers characterized by narrow wells with infinitely thin separators. This concept is also applicable to other wave-based modeling techniques. The approach is validated by comparing numerical results for Schroeder diffusers to measured data. In addition, it is proposed that irregular surfaces are modeled by shaping them with Brownian noise, giving good control over the sound scattering properties of the simulated boundary through two parameters, namely the spectral density exponent and the maximum well depth.

Many spectral analysis and modification techniques require the separation of sinusoidal from nonsinusoidal signal components of a Fourier spectrum. Techniques exist for the estimation of the parameters of nonstationary sinusoids, and for discriminating these from other components, within a single Fourier frame. We present a comparative study of five methods for sinusoidal discrimination, considering their effectiveness and their computational cost.

Both digital waveguide and finite difference techniques are numerical methods that have been demonstrated as appropriate for acoustic modelling applications. Whilst the application of the digital waveguide mesh to vocal tract modelling has been the subject of previous work, the application of comparable finite difference techniques is as yet untested. This study explores the characteristics of such a finite-difference approach to two-dimensional vocal tract modelling. Initial results suggest that finite difference techniques alone are not ideal, due to the limitation of non-dynamic behaviour and poor representation of admittance discontinuities in the approximation of threedimensional geometries. They do however introduce robust boundary formulations, and have a valid and useful application in modelling non-vital static volumes, particularly the nasal tract.

The digital waveguide mesh can be used to simulate the propagation of sound waves in an acoustic system. The accurate simulation of the acoustic characteristics of boundaries within such a system is an important part of the model. One significant property of an acoustic boundary is its diffusivity. Previous approaches to simulating diffuse boundaries in a digital waveguide mesh are effective but exhibit limitations and have not been analyzed in detail. An improved technique is presented here that simulates diffusion at boundaries and offers a high degree of control and consistency. This technique works by rotating wavefronts as they pass through a special diffusing layer adjacent to the boundary. The waves are rotated randomly according to a chosen probability function and the model is lossless. This diffusion model is analyzed in detail, and its diffusivity is quantified in the form of frequency dependent diffusion coefficients. The approach used to measuring boundary diffusion is described here in detail for the 2-D digital waveguide mesh and can readily be extended for the 3-D case.

Time domain articulatory vocal tract modeling in one-dimensional (1-D) is well established. Previous studies into two-dimensional (2-D) simulation of wave propagation in the vocal tract have shown it to present accurate static vowel synthesis. However, little has been done to demonstrate how such a model might accommodate the dynamic tract shape changes necessary in modeling speech. Two methods of applying the area function to the 2-D digital waveguide mesh vocal tract model are presented here. First, a method based on mapping the cross-sectional area onto the number of waveguides across the mesh, termed a widthwise mapping approach is detailed. Discontinuity problems associated with the dynamic manipulation of the model are highlighted. Second, a new method is examined that uses a static-shaped rectangular mesh with the area function translated into an impedance map which is then applied to each waveguide. Two approaches for constructing such a map are demonstrated; one using a linear impedance increase to model a constriction to the tract and another using a raised cosine function. Recommendations are made towards the use of the cosine method as it allows for a wider central propagational channel. It is also shown that this impedance mapping approach allows for stable dynamic shape changes and also permits a reduction in sampling frequency leading to real-time interaction with the model

The digital waveguide mesh is a discrete-time simulation used to model acoustic wave propagation through a bounded medium. It can be applied to the simulation of the acoustics of rooms through the generation of impulse responses suitable for auralization purposes. However, large-scale three-dimensional mesh structures are required for high quality results. These structures must therefore be efficient and also capable of flexible boundary implementation in terms of both geometrical layout and the possibility for improved mesh termination algorithms. The general one-dimensional N-port boundary termination is investigated, where N depends on the geometry of the modeled domain and the mesh topology used. The equivalence between physical variable Kirchoff-model, and scattering-based wave-model boundary formulations is proved. This leads to the KW-hybrid one-dimensional N-port boundary-node termination, which is shown to be equivalent to the Kirchoff- and wave-model cases. The KW-hybrid boundary-node is implemented as part of a new hybrid two-dimensional triangular digital waveguide mesh. This is shown to offer the possibility for large-scale, computationally efficient mesh structures for more complex shapes. It proves more accurate than a similar rectilinear mesh in terms of geometrical fit, and offers significant savings in processing time and memory use over a standard wave-based model. The new hybrid mesh also has the potential for improved real-world room boundary simulations through the inclusion of additional mixed modeling algorithms

A two-dimensional physical model of the human vocal tract is described. Such a system promises increased realism and control in the synthesis of both speech and singing. However, the parameters describing the shape of the vocal tract while in use are not easily obtained, even using medical imaging techniques, so instead a genetic algorithm (GA) is applied to the model to find an appropriate configuration. Realistic sounds are produced by this method. Analysis of these, and the reliability of the technique (convergence properties) is provided.

Digital waveguide physical modeling is often used as an efficient representation of acoustical resonators such as the human vocal tract. Building on the basic one-dimensional (1-D) Kelly-Lochbaum tract model, various speech synthesis techniques demonstrate improvements to the wave scattering mechanisms in order to better approximate wave propagation in the complex vocal system. Some of these techniques are discussed in this paper, with particular reference to an alternative approach in the form of a two-dimensional waveguide mesh model. Emphasis is placed on its ability to produce vowel spectra similar to that which would be present in natural speech, and how it improves upon the 1-D model. Tract area function is accommodated as model width, rather than translated into acoustic impedance, and as such offers extra control as an additional bounding limit to the model. Results show that the two-dimensional (2-D) model introduces approximately linear control over formant bandwidths leading to attainable realistic values across a range of vowels. Similarly, the 2-D model allows for application of theoretical reflection values within the tract, which when applied to the 1-D model result in small formant bandwidths, and, hence, unnatural sounding synthesized vowels.

The digital waveguide mesh is a modeling technique suitable for simulation of wave propagation in an acoustic system. Artificial boundary conditions are constructed for the digital waveguide mesh. Absorbing boundary conditions are evaluated and a new method for adjusting the reflection coefficient at values 0/spl les/r/spl les/1 is introduced. The frequency dependent error level of this method is minimized by the use of a second-order FIR filter.