This practice-based PhD consists of a portfolio of creative work and a supporting commentary. The portfolio illustrates the design decisions relating to my digital music performance system, and focuses upon the visibility and the fluidity of digital music performance. The goal of the design is to enhance the visibility without violating the audience’s auditory imagination unnecessarily, and to enhance the fluidity without relinquishing the unique fixed nature of digital music. The performance system consists of an audio engine, control mapping engine and visual engine. The audio engine and the control mapping engine were programmed with Cycling ‘74 Max. They let the performer deconstruct and reconstruct pre-recorded audio files with her/his hands via MIDI controllers during performance. The visual engine was programmed with Derivative TouchDesigner. In various ways, it visualises and exaggerates the performer’s actions which cause sonic changes, and filters out the rest. The works are presented as videos and the supporting commentary, deals with the contexts and thinking processes which determined the current performance system. By exploring theories of electronic music performance, audiovisual, visual music, acousmatic and medium specificity, I aim to explain the reasoning behind the performance system.

My original contribution to knowledge is a portfolio of 29 compositions written for the open world videogame Apotheon that constitutes an improvement to the effectiveness and implementation of recombinant videogame music. This portfolio was developed in response to the criticisms of multiple authors such a K. Collins, W. Phillips, S. Huiberts, A. Burnt, D. Raybould, R. Stevens, and others on the negative effects of excessive use of looping in video game music. A collaboration between myself and the programmer and game designer Lee Vermeulen brought the development of a new stochastic recombinant music engine that was implemented in Apotheon. The purpose of the engine is to replace continuous linear looping with unique musical variations in key areas of the game in which players might spend large amounts of time. The music in these areas is dynamically recombined in multiple independent layers using weighted probabilities that are altered according to the development of the narrative. The portfolio was inspired by aleatoric techniques found in 18th century musical dice games, and expanded on stochastic recombinant techniques found in earlier videogame soundtracks such as Ballblazer, Times of Lore and Legend of Zelda: Ocarina of Time.

Data-driven sequence models have long played a role in the analysis and generation of musical information. Such models are of interest in computational musicology, computer-aided music composition, and tools for music education among other applications. This dissertation beginswith an experiment tomodel sequences of musical pitch in melodies with a class of purely data-driven predictive models collectively known as Connectionist models. It was demonstrated that a set of six such models could performon par with, or better than state-of-the-art n-gram models previously evaluated in an identical setting. A new model known as the Recurrent Temporal Discriminative Restricted Boltzmann Machine (RTDRBM), was introduced in the process and found to outperform the rest of the models. A generalisation of this modelling task was also explored, and involved extending the set of musical features used as input by the models while still predicting pitch as before. The improvement in predictive performance which resulted from adding these new input features is encouraging for future work in this direction. Based on the above success of the RTDRBM, its application was extended to a non-musical sequence labelling task, namely Optical Character Recognition. This extension involved a modification to the model’s original prediction algorithm as a result of relaxing an assumption specific to the melody modelling task. The generalised model was evaluated on a benchmark dataset and compared against a set of 8 baseline models where it faired better than all of them. Furthermore, a theoretical extension to an existingmodel which was also employed in the above pitch prediction task - the Discriminative Restricted Boltzmann Machine (DRBM) - was proposed. This led to three new variants of the DRBM (which originally contained Logistic Sigmoid hidden layer activations), withHyperbolic Tangent, Binomial and Rectified Linear hidden layer activations respectively. The first two of these have been evaluated here on the benchmark MNIST dataset and shown to perform on par with the original DRBM.

This thesis presents the development of a software-based decoder design tool (DDT) for producing Ambisonic decoders optimised for playback over 5-speaker layouts. The research specifically focuses on developing decoders for irregular layouts with loudspeakers at a constant radial distance from the central listening position. It was motivated by the desire to provide better surround sound over the standard ITU 5-speaker layout for listeners in the sweet spot and off-centre positions. A wide-ranging literature review is presented revealing the need for such work. The DDT employs the Tabu Search algorithm to seek improved decoder parameters according to a multi-objective fitness function. The fitness function encapsulates criteria from psychoacoustic models as a set of objectives. In order to ensure the objectives were treated equally a method known as „range-removal‟ was used for the first time in Ambisonic decoder design. A companion technique termed „importance‟ allows the systematic prioritisation of range-removed objectives giving a designer control over desired decoder criteria. Additional elements exist in the DDT that can be turned on or off in different combinations. They include: a novel component for producing decoders with even performance by angle, a novel component for producing performance that correlates with the pattern of human spatial resolution estimated in previous Minimum Audible Angle experiments, and the ability to produce frequency dependent or independent decoders of different orders. Moreover, the user of the DDT can optimise performance for a single listener or multiple distributed listeners. To make the DDT as interactive as possible searches can optionally run on a High Performance Computer. This thesis also details the extensive testing of Ambisonic decoders for the ITU layout. Decoders have been assessed subjectively in listening tests and objectively using binaural measurements which has verified the methods developed in this research and the DDT‟s concept. Furthermore, decoders derived by the DDT have been compared to existing decoders and the results show they give equal or better performance. The development of a fully-functioning DDT which incorporates techniques for range-removal, importance, even performance by angle, minimum audible angle, off-centre listeners and their use in any combination represent the key outcomes of this work.