BATES TheCompositionAndPerformanceOfSpatialMusic

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  • The Composition and Performance

    of Spatial Music

    A dissertation submitted to the University of Dublin for the degree of Doctor of

    Philosophy

    Enda Bates Trinity College Dublin, August 2009.

    Department of Music &

    Department of Electronic and Electrical Engineering

    Trinity College Dublin

  • ii

    Declaration

    I hereby declare that this thesis has not been submitted as an exercise for a degree at

    this or any other University and that it is entirely my own work.

    I agree that the Library may lend or copy this thesis upon request.

    Signed,

    ___________________

    Enda Bates

  • iii

    Summary

    The use of space as a musical parameter is a complex issue which involves a

    number of different, yet interrelated factors. The technical means of performance, the

    sonic material, and the overall musical aesthetic must all work in tandem to produce a

    spatial impression in the listener which is in some way musically significant.

    Performances of spatial music typically involve a distributed audience and often take

    place in an acoustically reverberant space. This situation is quite different from the

    case of a single listener at home, or the composer in the studio. As a result, spatial

    strategies which are effective in this context may not be perceived correctly when

    transferred to a performance venue. This thesis examines these complex issues in

    terms of both the technical means of spatialization, and the compositional approach to

    the use of space as a musical parameter. Particular attention will be paid to the

    effectiveness of different spatialization techniques in a performance context, and what

    this implies for compositional strategies which use space as a musical parameter.

    Finally, a number of well known works of spatial music, and some original

    compositions by the author, are analyzed in terms of the perceptual effectiveness of

    the spatialization strategy.

    The results of a large number of listening tests and simulations were analysed

    to determine the fundamental capabilities of different spatialization techniques under

    the less than ideal conditions typically encountered during a performance. This

    analysis focussed on multichannel stereophony, Ambisonics, and Wavefield

    Synthesis. Other methods which are orientated toward a single listener are not

    addressed in this thesis. The results indicated that each spatialization scheme has

    particular strengths and weaknesses, and that the optimum technique in any situation

    is dependent on the particular spatial effect required. It was found that stereophonic

    techniques based on amplitude panning provided the most accurate localization but

    suffered from a lack of spaciousness and envelopment. Ambisonics provided an

    improved sense of envelopment but poor localization accuracy, particularly with first

    order Ambisonics systems. Consequently it would appear that stereophony is

    preferable when the directionality and focus of the virtual source is paramount, while

    Ambisonics is preferable if a more diffuse enveloping sound field is required.

    Ambisonics was consistently preferred for dynamically moving sources as this

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    technique eliminated the panning artefacts exhibited by amplitude panning as the

    source moves from a position at a loudspeaker, to one inbetween a pair of

    loudspeakers. The decoding scheme and order of the Ambisonics system also has a

    significant effect on the perceptual performance of the system, particularly at off-

    centre listener positions. A single-band, max-rE decoding scheme was found to be the

    most suitable approach for a distributed audience, and increasing the order of the

    system was shown to improve the performance at all listener positions. It is

    recommended that an octagonal array be adopted as a minimum standard for

    performances of multichannel spatial music, as this arrangement can be utilized for

    higher order Ambisonics and can also be readily implemented with digital audio

    hardware.

    Wavefield synthesis (WFS) was found to be quite distinct from multichannel

    techniques such as stereophony or Ambisonics. The spatial aliasing frequency is a

    critical aspect of any WFS system and localization errors and timbral distortions

    significantly increase if this parameter is too low. The ability of WFS systems to

    position virtual sources both behind and in front of the loudspeaker array was shown

    to be extremely difficult to achieve, particularly if the listeners position is fixed or if

    the performance space contains significant early reflections and reverberation.

    In the latter half of this thesis, a number of landmark works of spatial music

    were presented and analysed in terms of the perceptual validity of their approach to

    spatialization. It was shown that many composers have used spatial distribution to

    improve the intelligibility of different layers of material, and this approach was found

    to agree with the findings of scientific research in the area of auditory cognition. The

    use of recognizable spatial motifs was shown to be highly difficult to implement, and

    complex, abstract spatial designs are only indirectly related to what is eventually

    perceived by the audience. A gestural approach to spatial music has its origins in the

    practice of diffusion, yet this approach is equally applicable to other aesthetics and

    would seem to be highly suitable for mixed-media electroacoustic works. The use of

    augmented instruments which map the actions of the performer to a spatialization

    algorithm would seem to be well suited to performances of mixed-media spatial

    music. In addition, the use of flocking algorithms to control spatialization and sound

    synthesis also appears to be a novel and effective techniques for the creation of

    spatially dynamic, electronic sounds.

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    Acknowledgements

    I am deeply grateful to my two supervisors, Dr. Dermot Furlong and Mr. Donnacha

    Dennehy, for all their support and guidance over the past four years. Without their

    incredible knowledge and encouragement, this thesis would not have been possible.

    I would also like to particularly thank Dr. Fionnuala Conway and Gavin Kearney for

    their help over the years, all those who took part in listening tests, and my colleagues

    at the Spatial Music Collective.

    Finally I am very grateful for the support of my family and friends, and all the

    students and staff of the Music and Media Technology course in Trinity College.

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    Table of Contents Summary ...................................................................................................................... iii

    Acknowledgements........................................................................................................v

    Table of Contents..........................................................................................................vi

    List of Figures ................................................................................................................x

    List of Tables ..............................................................................................................xiv

    1 Introduction.................................................................................................................1

    1.1 Spatial Music: A Personal Perspective ................................................................1

    1.1.1 What Now in the Age of Disillusionment.....................................................2

    1.1.2 Why Spatial Music?......................................................................................3

    1.1.3 Why Talk About Spatial Hearing?................................................................5

    1.1.4 The Imaginative Use of Empirical Thinking ................................................6

    1.2 The Research Question ........................................................................................7

    1.3 Aims and Objectives ............................................................................................8

    1.4 Methodology........................................................................................................8

    1.5 Motivation............................................................................................................9

    1.6 Outline................................................................................................................10

    2 Spatial Hearing..........................................................................................................13

    2.1 Directional Hearing............................................................................................14

    2.2 Directional Hearing and Acoustics ....................................................................19

    2.3 Distance Hearing & Moving Sources ................................................................22

    2.3.1 Summary of Spatial Hearing.......................................................................25

    2.4 Spatial Hearing with Multiple Sources ..............................................................26

    2.4.1 The Limits of Auditory Perception .............................................................28

    2.4.2 Spatial Hearing and Virtual Sources............................