Alex Southern

Spatial Encoding of Finite Difference Time Domain Acoustic Models for Auralization

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

Methods for 2 nd Order Spherical Harmonic Spatial Encoding in Digital Waveguide Mesh Virtual Acoustic Simulations

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Sound propagation methods for road traffic noise auralization

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.

A method for plausible road tyre noise auralization

The Digital Waveguide Mesh (DWM) is a numerical simulation technique that has been shown to be suitable for modelling the acoustics of enclosed spaces. Previous work considered an approach using an array of spatially distributed receivers based on sound intensity probe theory to capture spatial room impulse responses (RIRs) from the DWM. A suitable process to facilitate spatial encoding of the DWMinto second-order spherical harmonics has also been explored. The purpose of this paper is to introduce a new alternative processing scheme based on the Blumlein Difference Technique. Both the previous and currently presented techniques are newly formulated with the main processing in the frequency domain. In addition the ability of the newly proposed technique for capturing the 2nd order components is confirmed and further processing of the receiver array is considered to extend the usable frequency range.

Sounding out smart cities: Auralization and soundscape monitoring for environmental sound design

When changes to an area involving an upgrade to a road network (new or existing) are planned, an assessment of the potential for change in the sound environment is carried out. However this assessment usually only considers local residents’ daily noise exposure and it can be difficult to understand what an increase of 2 dB, for example, actually means in terms of what you hear. Further to this, perceived changes in sound character in relation to road traffic and associated noise mitigation measures are not assessed by current methodologies. There has been increased interest recently in auralization as a potential environmental sound design tool. Without the existence of standardized guidance on the application of existing sound propagation models for auralization there is a potential to obtain a wide range of perceptually different results, depending on the adopted methodology. This work discusses important considerations for the auralization of road traffic noise. Accurately creating these experiences re...

Modeling reflections from rough surfaces in complex spaces

Interest in research relating to the impact and abatement of road traffic noise has increased since the Environmental Noise Directive was introduced. The World Health Organisation has recognized road traffic noise as a serious problem for public health, and annoyance with some aspect of our daily soundscape is well recognized as a common complaint. Auralization tools can allow designers, planners and relevant stakeholders to listen and converse on human response to a planned development or mitigation strategy. An ideally detailed road traffic noise auralization system would render the acoustic emission of every vehicle on the road network at any desired receptors. This work focuses on the sound emission from the road tyre interaction for the purpose of auralization and extends on previous work for synthesising road tyre noise based on a small dataset of roadside recordings. The proposed method discussed in comparison to a recently published approach and the plausibility of the proposed method is verified.

Diffusing boundaries in the digital waveguide mesh and their effect on reverberation time

Auralization is key in developing a better understanding of how significant changes or infrastructure planning in our urban environment can have an impact on our related environmental soundscape. It allows consultants, planners and other stakeholders to hear the potential acoustic changes that might result, so that designs might be better optimized; it is also a valuable dissemination tool for informing the public as to the nature of such changes. Auralization also facilitates subjective soundscape assessment of proposed developments at the design stage and once construction is complete, smart sensor networks enable soundscape monitoring and objective evaluated on an ongoing basis. Of particular interest is sound emitted from transportation, as it is generally considered as unwanted sound and hence defined as noise. Transportation noise and road traffic noise in particular, is considered a concern for public health by the WHO, and annoyance with some aspect of our daily soundscape is not uncommon. This wo...

Rendering walk-through auralisations using wave-based acoustical models

Acoustic reflections from rough surfaces occur both in indoor and outdoor environments. Detailed modeling of such reflections is possible with wave-based modeling algorithms. However, their time and resource consumption limits the applicability of such algorithms in practical modeling tasks where the modeled space is large or even unbounded. On the other hand, geometrical acoustics modeling techniques are more efficient in most cases, but they are not able to capture the wave interaction with the rough surface. The presented solution combines a geometric modeling algorithm with a theoretical model of the rough surface. The geometric algorithm is an efficient beam tracer. The theoretical model assumes long wavelength compared to the dimensions of the surface details. The model shows that the effect of the rough surface can be approximated with a exponential decay tail after an impulse in the time domain impulse response. A further approximation is to present multiple such reflections with a decay resemblin...

Spatial high frequency extrapolation method for room acoustic auralization

The digital waveguide mesh is often used to simulate the propagation of sound waves in an acoustic system. The diffusing layer is an approach that has been shown as appropriate for simulating diffuse boundary reflections as this is a fundamental acoustic property of real surfaces. Incoming wavefronts are rotated randomly according to a chosen probability function at a layer of mesh nodes adjacent to the boundary of interest. Although this method offers a high level of control and consistency, the nature of the interaction between terminating boundary function and incident wave is altered with an associated potential impact on the resultant wave propagation behaviour for the rest of the space. This paper explores this effect based on impulse response measurements obtained from a simulated space. Results are presented demonstrating the effect diffusion modelling has on early reflections and that depending on the conditions imposed increased boundary diffusivity can lead to either an increase or decrease in reverberation time. Standard objective measures are used to demonstrate the perceptual effect of increased boundary diffusivity on the spatially encoded diffuse field for the modelled space.