Dr Martin Dewhirst
Lecturer (IoSR)
Qualifications: MMath, PhD (Surrey)
Email: martin.dewhirst@surrey.ac.uk
Phone: Work: 01483 68 6505
Room no: 05 BC 03
Further information
Biography
Dr Martin Dewhirst joined the University as a Lecturer in August 2009. Martin's teaching focuses on signal processing, sound synthesis and computer audio systems.
Prior to being appointed as lecturer, Martin was worked as a Research Assistant on the QESTRAL research project, a collaboration between the University of Surrey's IoSR and CVSSP, Bang & Olufsen and BBC Research and Development. The aim of this project was to develop an objective measure of the spatial quality of spatial audio processing systems. While working on the QESTRAL project, Martin also completed his PhD at the University of Surrey, with a thesis titled Modelling perceived spatial attributes of reproduced sound. His current research interests include the relationship between audio quality and lower level perceptual attributes, subjective testing and modelling the perceived spatial attributes of reproduced sound using objective measurements.
A publications list is available here
email: martin.dewhirst@surrey.ac.uk
Publications
Journal articles
- . (2010) 'Development and validation of an unintrusive model for predicting the sensation of envelopment arising from surround sound recordings'. AES: Journal of the Audio Engineering Society, 58 (12), pp. 1013-1031.
Conference papers
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(2010) 'Estimates of perceived spatial quality across the listening area'. Proceedings of the AES International Conference, , pp. 233-242.Full text is available at: http://epubs.surrey.ac.uk/7691/
Abstract
This paper describes a computational model for the prediction of perceived spatial quality for reproduced sound at arbitrary locations in the listening area. The model is specifically designed to evaluate distortions in the spatial domain such as changes in source location, width and envelopment. Maps of perceived spatial quality across the listening area are presented from our initial results.
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(2008) 'QESTRAL (Part 4): Test signals, combining metrics and the prediction of overall spatial quality'. Audio Engineering Society San Francisco CA: 125th Audio Engineering Society ConventionFull text is available at: http://epubs.surrey.ac.uk/7762/
Abstract
The QESTRAL project has developed an artificial listener that compares the perceived quality of a spatial audio reproduction to a reference reproduction. Test signals designed to identify distortions in both the foreground and background audio streams are created for both the reference and the impaired reproduction systems. Metrics are calculated from these test signals and are then combined using a regression model to give a measure of the overall perceived spatial quality of the impaired reproduction compared to the reference reproduction. The results of the model are shown to match closely the results obtained in listening tests. Consequently, the model can be used as an alternative to listening tests when evaluating the perceived spatial quality of a given reproduction system, thus saving time and expense.
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(2008) 'QESTRAL (Part 3): system and metrics for spatial quality prediction'. Audio Engineering Society San Francisco CA: 125th Audio Engineering Society ConventionFull text is available at: http://epubs.surrey.ac.uk/7761/
Abstract
The QESTRAL project aims to develop an artificial listener for comparing the perceived quality of a spatial audio reproduction against a reference reproduction. This paper presents implementation details for simulating the acoustics of the listening environment and the listener’s auditory processing. Acoustical modeling is used to calculate binaural signals and simulated microphone signals at the listening position, from which a number of metrics corresponding to different perceived spatial aspects of the reproduced sound field are calculated. These metrics are designed to describe attributes associated with location, width and envelopment attributes of a spatial sound scene. Each provides a measure of the perceived spatial quality of the impaired reproduction compared to the reference reproduction. As validation, individual metrics from listening test signals are shown to match closely subjective results obtained, and can be used to predict spatial quality for arbitrary signals.
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(2008) 'QESTRAL (Part 2): Calibrating the QESTRAL model using listening test data'. Audio Engineering Society Proc. 125th AES Conv., San Francisco CA, San Francisco USA: 125th AES ConventionFull text is available at: http://epubs.surrey.ac.uk/7737/
Abstract
The QESTRAL model is a perceptual model that aims to predict changes to spatial quality of service between a reference system and an impaired version of the reference system. To achieve this, the model required calibration using perceptual data from human listeners. This paper describes the development, implementation and outcomes of a series of listening experiments designed to investigate the spatial quality impairment of 40 processes. Assessments were made using a multi-stimulus test paradigm with a label-free scale, where only the scale polarity is indicated. The tests were performed at two listening positions, using experienced listeners. Results from these calibration experiments are presented. A preliminary study on the process of selecting of stimuli is also discussed.
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(2008) 'QESTRAL (Part 1): Quality Evaluation of Spatial Transmission and Reproduction using an Artificial Listener'. Proc. 125th AES Conv., San Francisco CA, Full text is available at: http://epubs.surrey.ac.uk/7736/
Abstract
Most current perceptual models for audio quality have so far tended to concentrate on the audibility of distortions and noises that mainly affect the timbre of reproduced sound. The QESTRAL model, however, is specifically designed to take account of distortions in the spatial domain such as changes in source location, width and envelopment. It is not aimed only at codec quality evaluation but at a wider range of spatial distortions that can arise in audio processing and reproduction systems. The model has been calibrated against a large database of listening tests designed to evaluate typical audio processes, comparing spatially degraded multichannel audio material against a reference. Using a range of relevant metrics and a sophisticated multivariate regression model, results are obtained that closely match those obtained in listening tests.
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(2005) 'Objective assessment of spatial localisation attributes of surround-sound reproduction systems'. Barcelona : Audio Engineering Society Sound: 108th AES ConventionFull text is available at: http://epubs.surrey.ac.uk/7753/