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 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 ii 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 iii 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 listener’s 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. iv 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. v 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...........................................................29 2.4.3 Spatial Audio Techniques...........................................................................30 3 Stereophony ..............................................................................................................32 3.1 Quadraphonic Sound..........................................................................................35 3.2 Cinema Surround Sound and 5.1 .......................................................................37 3.3 Multichannel Amplitude Panning Techniques...................................................38