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Virtual acoustic environments for the evaluation of hearing devices

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thesis
posted on 28.03.2022, 11:30 by Christos Oreinos
Listening tests are essential for optimising and evaluating novel signal processing concepts for hearing devices. When they are performed inside the laboratory they are highly controlled, but typically lack ecological validity. On the other hand, field-studies provide high ecological validity, but are difficult to control, time-consuming and costly. Even though field-studies may ultimately be required, there still is a necessity for more realistic laboratory-based listening tests. This thesis focuses on creating and validating realistic virtual sound environments (VSEs), primarily based on the method of higher-order Ambisonics (HOA), for testing hearing aids (HAs). Particular emphasis has been given on how the VSE limitations affect the output of multi-microphone directional HAs. To systematically and objectively analyse the errors incurred by such VSEs, we developed and verified a framework that consists of: (1) the simulation of a reverberant acoustic scene; (2) the coding of that scene using HOA; (3) the reconstruction of the VSE via a loudspeaker array; and (4) the evaluation of the SNR benefit and output pressure of directional HAs worn on an acoustic manikin placed inside the VSE. A listening experiment was additionally designed to test the simulation results. For that purpose, a real-room 'cocktail-party' acoustic scene was created and acoustically modelled. Ambisonics was then applied to reproduce that scene inside a loudspeaker array. Listening tests involving hearing-impaired subjects, fitted with directional HAs, were next conducted inside the real and the virtual sound environments. The intelligibility and acceptable-noise-level benefits of the directional HAs were thereby estimated. The above evaluation illustrated that most of the real-environment properties can be faithfully reconstructed by the considered VSEs. Moreover, directional HA algorithms were shown to behave and adapt in a similar way as in real environments. However, sound-field reconstruction deviations were noticeable. For the case of highly directional schemes, such as the considered bilateral beamformer, such deviations may result in a reduced benefit estimation. Hence, we can conclude that although the described VSEs illustrated a reduced sensitivity in demonstrating real-life benefits, they are nonetheless suitable for evaluating directional HA processing schemes.

History

Table of Contents

1. Introduction -- 2. The theory of higher-order ambisonics -- 3. Measurement of a full 3D set of HRTFs for in-ear and hearing aid microphones on a head and torso simulator (HATS) -- 4. Objective analysis of ambisonics for hearing aid applications : effect of listener's head, room reverberation, and directional microphones -- 5. Effect of higher-order ambisonics on evaluating beamformer benefit in realistic acoustic environments -- 6. An objective and subjective validation of applied loudspeaker-based virtual sound environments used for directional hearing and testing -- 7. Concluding discussion.

Notes

Theoretical thesis. Bibliography: pages 157-169 "A thesis submitted in fulfilment of the requirements for the degree of Doctor of Philosophy at the National Acoustic Laboratories & Department of Linguistics, Faculty of Human Sciences" -- title page.

Awarding Institution

Macquarie University

Degree Type

Thesis PhD

Degree

PhD, Macquarie University, Faculty of Human Sciences, Department of Linguistics

Department, Centre or School

Department of Linguistics

Year of Award

2015

Principal Supervisor

Jörg M. Buchholz

Additional Supervisor 1

Jorge Mejia

Rights

Copyright Christos Oreinos 2015.

Language

English

Extent

xxii, 169 pages colour illustrations

Former Identifiers

mq:70965 http://hdl.handle.net/1959.14/1269481