Thomas McKenzie

• Doctor of Philosophy
• Lecturer at University of Edinburgh

Ambisonics has enjoyed a recent resurgence in popularity due to virtual reality applications. Low order Ambisonic reproduction is inherently inaccurate at high frequencies, which causes poor timbre and height localisation. Diffuse-Field Equalisation (DFE), the theory of removing direction-independent frequency response, is applied to binaural (over...

Although the difference between the fast Fourier transforms of two audio signals is often used as a basic measure of predicting perceived colouration, these signal measures do not provide information on how relevant the results are from a perceptual point of view. This paper presents a perceptually motivated loudness calculation for predicting the...

This article proposes a system for object-based six-degrees-of-freedom (6DoF) rendering of spatial sound scenes that are captured using a distributed arrangement of multiple Ambisonic receivers. The approach is based on first identifying and tracking the positions of sound sources within the scene, followed by the isolation of their signals through...

This exploratory study investigates the phenomenon of the auditory perceived aperture position (APAP): the point at which one feels they are in the boundary between two adjoined spaces, judged only using auditory senses. The APAP is likely the combined perception of multiple simultaneous auditory cue changes, such as energy, reverberation time, env...

The evaluation of audio quality is important in the development of immersive audio algorithms and reproduction systems, and binaural models are often used for this as a quick alternative to listening tests. Coloration (i.e., perceived loudness differences integrated across ears and frequency) is one key quality aspect; however, the majority of mode...

Typically, evaluation of spatial audio systems uses the same source signal for each condition in listening comparison tests (such as ABX and MUSHRA). However in an augmented reality scenario, it is unlikely that the exact same source signal would exist at the exact same position in space, both real and virtual: instead, a real source would be in on...

The inner auditory experience comprises various sounds which, rather than originating from sources in their environment, form as a result of internal processes within the brain of an observer. Examples of such sounds are, for instance, verbal thoughts and auditory hallucinations. Traditional audiovisual media representations of inner voices have te...

To auralize a room's acoustics in six degrees-of-freedom virtual reality (VR), a dense set of spatial room impulse response (SRIR) measurements is required, so interpolating between a sparse set is desirable. This paper studies the auralization of room transitions by proposing a baseline interpolation method for higher-order Ambisonic SRIRs and eva...

Measured spatial room impulse responses (SRIRs) are often used for realistic six degrees-of-freedom (6DoF) virtual reality applications, as they allow for the high quality capture and reproduction of a room's acoustics. Dense sets of SRIR measurements are time consuming to acquire, especially for multiple source and receiver combinations, and so in...

The acoustics of coupled rooms is often more complex than single rooms due to the increase in features such as double-slope decays, direct sound occlusion and anisotropic reverberation. For directional capture, analysis and reproduction of room acoustics, spatial room impulse responses (SRIRs) can be utilised, but measuring SRIRs at multiple positi...

The spatial speech reproduction capabilities of a KEMAR mouth simulator, a loudspeaker, the piston on the sphere model, and a circular harmonic fitting are evaluated in the near-field. The speech directivity of 24 human subjects, both male and female, is measured using a semicircular microphone array with a radius of 36.5 cm in the horizontal plane...

Acoustically transparent head-worn devices are a key component of auditory augmented reality systems, in which both real and virtual sound sources are presented to a listener simultaneously. Head-worn devices can exhibit a high transparency simply through their physical design but in practice will always obstruct the sound field to some extent. In...

Spatial room impulse responses (SRIRs) capture room acoustics with directional informa- tion. SRIRs measured in coupled rooms and spaces with non-uniform absorption distribution may exhibit anisotropic reverberation decays and multiple decay slopes. However, noisy mea- surements with low signal-to-noise ratios pose issues in analysis and reproducti...

The sound field in coupled rooms or rooms with non-uniform absorptive material distributions can be considerably anisotropic. In such scenarios, the sound energy decays with more than one decay rate, thus making it practical to use a decay model that consists of multiple exponential decays and a noise term. In this work, we use a recently proposed...

For the evaluation of virtual acoustics for mixed realities, we distinguish between the paradigms 'authenticity', 'plausibility' and 'transfer-plausibility'. In the case of authenticity, discrimination tasks between real sound sources and virtual renderings presented over headphones are performed, whereas in case of a plausibility experiment, liste...

Room acoustics measurements are used in many areas of audio research, from physical acoustics modelling and speech enhancement to virtual reality applications. This paper documents the technical specifications and choices made in the measurement of a dataset of spatial room impulse responses (SRIRs) in a variable acoustics room. Two spherical micro...

Room acoustics measurements are used in many areas of audio research, from physical acoustics modelling and speech enhancement to virtual reality applications. This paper documents the technical specifications and choices made in the measurement of a dataset of spatial room impulse responses (SRIRs) in a variable acoustics room. Two spherical micro...

The perceptual experience of the transition between coupled rooms remains a little investigated area of research. This paper presents a pipeline for auralising the transition between coupled rooms, utilising a time-varying partitioned convolution for fast position-dependent switching between spatial room impulse responses (SRIRs) and parametric bin...

--- Download link: http://etheses.whiterose.ac.uk/26445/ --- Humans can localise sounds in all directions using three main auditory cues: the differences in time and level between signals arriving at the left and right eardrums (interaural time difference and interaural level difference, respectively), and the spectral characteristics of the sign...

Binaural Ambisonic rendering can be achieved using virtual loudspeakers through head-related impulse response (HRIR) convolution of the Ambisonic loudspeaker feeds. It is widely used in immersive applications such as virtual reality due to its sound field rotation capabilities and low channel count. Binaural Ambisonic reproduction is inaccurate at...

In virtual reality applications, where Ambisonic audio is presented to the user binaurally (over headphones) in conjunction with a head-mounted display, retained immersion relies on congruence between the auditory and visual experiences. Therefore frontal accuracy of binaural Ambisonic audio is an area of interest. A previously introduced method fo...

The increasing popularity of Ambisonics as a spatial audio format for streaming services poses new challenges to existing audio coding techniques. This paper seeks to evaluate timbral distortion and localization accuracy of Ambisonic audio encoded using Opus low-bitrate compression. The study was conducted for 1 st , 3 rd and 5 th order Ambisonic s...

Binaural Ambisonic rendering is widely used in immersive applications such as virtual reality due to its sound field rotation capabilities. An issue of low-order Ambisonics is that interaural level differences (ILDs), a crucial cue for horizontal localisation, are often reproduced lower than they should be, which reduces lateralisation. This paper...

Featured Application The methods presented in this paper improve high-frequency reproduction of binaural Ambisonic rendering. Abstract Ambisonics is a spatial audio technique appropriate for dynamic binaural rendering due to its sound field rotation and transformation capabilities, which has made it popular for virtual reality applications. An iss...

The human auditory system is more accurate at localising sounds in front than at lateral, rear and elevated directions. In virtual reality applications, where Ambisonic audio is presented to the user binaurally (over headphones) in conjunction with a head-mounted display, it is imperative that audio in the frontal direction is as accurate as possib...

In audio engineering research, repeatability is paramount. Speech is a great stimulus to use when evaluating audio systems, as it is a real world sound highly familiar to the human auditory system. With a view to the comparison of real and simulated sound fields, a repeatable speech source is therefore highly beneficial. This paper presents both an...

Timbre is a crucial element of believable and natural binaural synthesis. This paper presents a method for diffuse-field equalisation of first-order Ambisonic binaural rendering, aiming to address the timbral disparity that exists between Ambisonic rendering and head related transfer function (HRTF) convolution, as well as between different Ambison...

In this paper, we investigate the perception of height cues in motion-tracked transaural reproduction. 10 subjects were asked to localise sounding objects with height in a two-loudspeaker head-tracked transaural reproduction setup. Features of the head related transfer function (HRTF) for height perception were tested with generic HRTFs from a KEMA...