Richard Hughes

University of Salford, Acoustics Research Centre, Graduate Student

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Postdoctoral researcher / engineer specialising in architectural acoustics and spatial audio reproduction, with additional experience in both academic and commercial fields. Previous work includes: numerical modelling of acoustic diffusers, scattering surfaces, room acoustics and outdoor noise propagation
Supervisors: Trevor Cox

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Papers by Richard Hughes

Fluttering Reverberance: Real Life Examples of Chaotic Billiards with Convex Sections

Proceedings of the ICA congress, 2019

Billiards are used to explore dynamical systems. The mathematical literature focusses on idealise... more Billiards are used to explore dynamical systems. The mathematical literature focusses on idealised physics and simple shapes like the Bunimovich stadium. Real enclosures where sound waves created by such shapes exhibit strong audible artefacts are uncommon. Also, billiard modelling is a high frequency approximation and diffraction is often important in rooms. Notwithstanding, some rare real-life acoustic billiards where the effects of closed-orbits are clearly audible have been found and examined with simulations and measurements. The abandoned Thurgoland railway tunnel in Yorkshire, UK has an extraordinary metallic flutter in its long reverberant decay. A booking hall in the National Theatre railway station in Oslo has a very strong warble, and sounds different to the flutter echo heard in a simple cylindrical space. Both spaces feature concave geometries: the Thurgoland tunnel has a horseshoe-shaped cross-section, whereas the Oslo station is a distorted cylinder in plan with a corrugated domed roof. Ray-tracing reveals closed orbits, which lead to repeated reflections and marked flutter echoes in both spaces. Examining the angles of the rays arriving at the receiver, and the autocorrelation of the impulse response envelope, provides further evidence of non-diffuseness. A Boundary Element Method is used to explore diffraction within the Thurgoland tunnel.

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An Audio-Visual System for Object-Based Audio: From Recording to Listening

IEEE Transactions on Multimedia, 2018

Object-based audio is an emerging representation for audio content, where content is represented ... more Object-based audio is an emerging representation for audio content, where content is represented in a reproductionformat-agnostic way and, thus, produced once for consumption on many different kinds of devices. This affords new opportunities for immersive, personalized, and interactive listening experiences. This paper introduces an end-to-end object-based spatial audio pipeline, from sound recording to listening. A high-level system architecture is proposed, which includes novel audiovisual interfaces to support object-based capture and listenertracked rendering, and incorporates a proposed component for objectification, that is, recording content directly into an object-based form. Text-based and extensible metadata enable communication between the system components. An open architecture for object rendering is also proposed. The system's capabilities are evaluated in two parts. First, listener-tracked reproduction of metadata automatically estimated from two moving talkers is evaluated using an objective binaural localization model. Second, object-based scene capture with audio extracted using blind source separation (to remix between two talkers) and beamforming (to remix a recording of a jazz group) is evaluated

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$Research paper thumbnail of Characterization of acoustic diffusion using refracto-vibrometry$

Characterization of acoustic diffusion using refracto-vibrometry

Journal of Sound and Vibration, 2017

Refracto-vibrometry is a relatively new measurement technique that is sensitive to variations in ... more Refracto-vibrometry is a relatively new measurement technique that is sensitive to variations in the optical refractive index of a medium caused by changes in acoustic pressure within that medium (the acousto-optic effect). It has so far been employed primarily as a qualitative visualization tool for airborne sound propagation because determining sound pressure level at a point using the technique is difficult and inefficient. Instead, the authors propose that this optical technique is well suited for determining dimensionless quantities, such as coefficients describing scattering uniformity from a surface. A new measurement and analysis process relying on refractovibrometry has been developed and used to determine acoustic diffusion coefficients through purely optical means for the first time. A quadratic residue diffuser is used as an arbitrary test surface, and refracto-vibrometry measurements of its polar response have been performed and results compared to a boundary element model. The benefits and limitations of the optical method over the traditional microphone-based approach are discussed.

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Evaluating a distortion-weighted glimpsing metric for predicting binaural speech intelligibility in rooms

A distortion-weighted glimpse proportion metric (BiDWGP) for predicting binaural speech intelligi... more A distortion-weighted glimpse proportion metric (BiDWGP) for predicting binaural speech intelligibility were evaluated in simulated anechoic and reverberant conditions, with and without a noise masker. The predictive performance of BiDWGP was compared to four reference binaural intelligibility metrics, which were extended from the Speech Intelligibility Index (SII) and the Speech Transmission Index (STI). In the anechoic sound field, BiDWGP demonstrated high accuracy in predicting binaural intelligibility for individual maskers (ρ ≥ 0.95) and across maskers (ρ ≥ 0.94). The reference metrics however performed less well in across-masker prediction (0.54 ≤ ρ ≤ 0.86) despite reasonable accuracy for individual maskers. In reverberant rooms, BiDWGP was more stable in all test conditions (ρ ≥ 0.87) than the reference metrics, which showed different predictive patterns: the binaural STIs were more robust for the stationary than for the fluctuating noise masker, whilst the binaural SII displayed the opposite behaviour. The study shows that the new BiDWGP metric can provide similar or even more robust predictive power than the current standard metrics.

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On object-based audio with reverberation

Object-based audio is gaining momentum as a means for future audio productions to be format-agnos... more Object-based audio is gaining momentum as a means for future audio productions to be format-agnostic and interactive. Recent standardization developments make recommendations for object formats, however the capture, production and reproduction of reverberation is an open issue. In this paper, we review approaches for recording, transmitting and rendering reverberation over a 3D spatial audio system. Techniques include channel-based approaches where room signals intended for a specific reproduction layout are transmitted, and synthetic reverberators where the room effect is constructed at the renderer. We consider how each approach translates into an object-based context considering the end-to-end production chain of capture, representation, editing, and rendering. We discuss some application examples to highlight the implications of the various approaches.

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Volumetric diffusers: Pseudorandom cylinder arrays on a periodic lattice

by Mark Pogson, Richard Hughes, and Jamie Angus

The Journal of the Acoustical Society of America, 2010

Most conventional diffusers take the form of a surface based treatment, and as a result can only ... more Most conventional diffusers take the form of a surface based treatment, and as a result can only operate in hemispherical space. Placing a diffuser in the volume of a room might provide greater efficiency by allowing scattering into the whole space. A periodic cylinder array ͑or sonic crystal͒ produces periodicity lobes and uneven scattering. Introducing defects into an array, by removing or varying the size of some of the cylinders, can enhance their diffusing abilities. This paper applies number theoretic concepts to create cylinder arrays that have more even scattering. Predictions using a boundary element method are compared to measurements to verify the model, and suitable metrics are adopted to evaluate performance. Arrangements with good aperiodic autocorrelation properties tend to produce the best results. At low frequency power is controlled by object size and at high frequency diffusion is dominated by lattice spacing and structural similarity. Consequently the operational bandwidth is rather small. By using sparse arrays and varying cylinder sizes, a wider bandwidth can be achieved.

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Fly Over Noise Measurements and Simulation for a Turboprop Aircraft

Presented at Internoise, Innsbuck (Austria), Sep 2013

The study of aircraft noise started in earnest in the 1960s, however, the validation of comprehen... more The study of aircraft noise started in earnest in the 1960s, however, the validation of comprehensive noise models for existing commercial aircraft using well defined experimental data have since produced modest advances. Considerable focus appears to have been placed on aircraft conceptual design, with relatively little effort considering aircraft currently in use, for which we believe there is a growing need. This study investigates the fly over noise from a commercial turboprop aircraft, using noise measurements taken both on airport departure and approach for the validation of noise simulations. Predictions are carried out using a software system described elsewhere in the literature. It is shown that, for the examples considered, predicted overall noise levels such as SEL and EPNL display modest agreement, and are within 4.3dB/EPNdB of measured values. One-third octave band analysis shows discrepancies to be due to a general under prediction at low to mid frequencies. Through an analysis of noise source subcomponents, the most likely candidates are identified for which an alteration in the model best improves agreement. By applying these alterations – in particular, by increasing the contribution of the landing gear and airframe noise – an average error in one-third octave band SPL of less than 3.2dB is achieved.

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Volume diffusers for architectural acoustics

Most conventional diffusers are used on room surfaces, and consequently can only operate on a hem... more Most conventional diffusers are used on room surfaces, and consequently can only operate on a hemispherical area. Placing a diffuser in the volume of a room may provide greater efficiency by allowing scattering into the whole space. There are very few examples of volume diffusers and they tend to be limited in design; subsequently a suitable method for their development is lacking.

2D volumetric diffusers are investigated, considering a number of design concepts; namely arrays of slats, percolation structures and cylinder arrays. An experimental technique is adapted for their measurement, and the results are used to verify prediction models for each type. Diffusive efficacy is assessed through a new metric based on an existing surface diffuser coefficient and a measure of scattered power requiring half of the energy to be back-scattered.

Single layer slat arrays are formed from optimal aperiodic sequences, though due to the directional scattering from individual slats at higher frequencies, performance is heavily dependent on line-of-sight through the array. This limits the operational bandwidth to approximately 1.5 octaves. Multi-layer structures offer improvements by allowing cancellation of the back-scattered lobe, though at high frequency the specular reflection from an individual slat still dominates. Percolation fractals use slats orientated in multiple directions and by scattering laterally can channel sound and diffuse at lower frequencies. Low frequency diffusion however is limited and the best structures are those which provide a broad range of geometric reflection paths.

Through application of number theoretic concepts, arrangements of cylinders are shown to offer more enhanced diffusing abilities than slat and percolation structures. At low frequency scattered power is controlled by cylinder size and at high frequency diffusion is dominated by their spacing. By minimising structural similarity and including cylinders with circumference comparable to wavelength, significant diffusion is achieved over an approximate 5 octave bandwidth.

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Volumetric diffusers: pseudorandom cylinder arrays on a periodic lattice

by Richard Hughes and Mark Pogson

The Journal of the …, Jan 1, 2010

Most conventional diffusers take the form of a surface based treatment, and as a result can only ... more Most conventional diffusers take the form of a surface based treatment, and as a result can only operate in hemispherical space. Placing a diffuser in the volume of a room might provide greater efficiency by allowing scattering into the whole space. A periodic cylinder array (or sonic crystal) produces periodicity lobes and uneven scattering. Introducing defects into an array, by removing or varying the size of some of the cylinders, can enhance their diffusing abilities. This paper applies number theoretic concepts to create cylinder arrays that have more even scattering. Predictions using a boundary element method are compared to measurements to verify the model, and suitable metrics are adopted to evaluate performance. Arrangements with good aperiodic autocorrelation properties tend to produce the best results. At low frequency power is controlled by object size and at high frequency diffusion is dominated by lattice spacing and structural similarity. Consequently the operational bandwidth is rather small. By using sparse arrays and varying cylinder sizes, a wider bandwidth can be achieved.

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Diffusive benefits of cylinders in front of a Schroeder diffuser

by Mark Pogson and Richard Hughes

The Journal of the …, Jan 1, 2010

A numerical investigation is performed into the diffusive effects of cylinders positioned in fron... more A numerical investigation is performed into the diffusive effects of cylinders positioned in front of a Schroeder diffuser. A regular line of cylinders is shown to offer notable improvements to diffusion from a periodic Schroeder device, provided lateral cylinder spacing is incommensurable with the Schroeder period width. Further investigation considers angular dependence and low frequency results in greater detail, as well as the effects on narrowband and modulated Schroeder devices. An optimization procedure is subsequently performed to investigate the effects of an irregular cylinder arrangement, which provides further diffusive benefits.

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Multiple scattering between cylinders and a Schroeder diffuser

by Richard Hughes and Mark Pogson

Acta Acustica united …, Jan 1, 2010

A multiple scattering method is developed to model an array of N cylinders positioned in front of... more A multiple scattering method is developed to model an array of N cylinders positioned in front of a Schroeder diffuser. Results are compared against the more computationally intensive boundary element method, as well as existing multiple scattering methods for cylinders alone. An investigation of scattering performance from a cylinder arrangement in front of a Schroeder diffuser is also performed. The addition of cylinders is shown to offer potential benefits such as reducing the effects of periodicity in the Schroeder diffuser.

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Volumetric diffusion from pseudorandom periodic cylinder arrays

Most conventional diffusers take the form of a surface based treatment, and as a result can only ... more Most conventional diffusers take the form of a surface based treatment, and as a result can only operate in hemispherical space. By placing a diffuser in the volume of a room, scattering into the whole space becomes possible, receiving from and scattering into all possible directions. This affords potential for greater efficiency. One candidate structure is the periodic cylinder array (or sonic crystal), but these produce inherent periodicity lobes and consequently provide uneven scattering. However introducing defects into an array, by removing individual cylinders, can enhance their performance. This paper applies number theoretic concepts to create cylinder arrays that have more even scattering. Predictions using the Boundary Element Method, with suitable metrics are used to evaluate their performance. Arrangements with good aperiodic autocorrelation properties tend to provide the best performance. Due to the underlying periodicity, there are frequencies at which lobing is unavoidable, and the equivalent to ‘flat-plate’ frequencies in Schroeder diffusers occurs due to specular redirection.

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$Research paper thumbnail of Volumetric diffusers inspired by percolation fractals$

Volumetric diffusers inspired by percolation fractals

by Richard Hughes and Mark Pogson

Proceedings of the Institute of Acoustics, Oct 3, 2008

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Volumetric Diffusers

aes.org

Although many types of diffusers have been proposed, they are predominantly surface treatment. Th... more Although many types of diffusers have been proposed, they are predominantly surface treatment. This paper places the diffuser in the volume of the room rather than on the surfaces, forming a volume based diffuser. In particular, we examine suitable sequences for their implementation. We also consider suitable metric’s to evaluate their performance. At first single layer volumetric diffusers are examined, and then multi-layer volumetric diffusers are investigated. In particular, the effects of varying the spacing, and number of layers, is more closely examined. The Boundary Element Method (BEM) model is used to gain accurate predictions of the diffuser’s performance. Finally, we demonstrate a diffusion structure that has a similar performance to that of a Primitive Root Diffuser (PRD).

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