Closing the Loop: Implementing Real-time Audio Feedback Systems in Musical Robots

A closed-loop control system is any configuration that feeds information about its output back into the control stream. These types of systems have been in use for hundreds of years in various engineering related disciplines to carry out operations such as keeping rooms at the correct temperature, implementing cruise control in cars, and precisely positioning industrial machinery. When a musician performs a piece, a type of biological closed loop is invoked in which the player continuously listens to the sound of their instrument, and adjusts their actions in order to ensure their performance is as desired. However, most musical robots do not possess this ability, instead relying on open-loop systems without feedback. This results in the need for much manual intervention from the operators of these robots, unintuitive control interfaces for composing and performing music with them, and tuning, timing, dynamics and other issues occurring during performances. This thesis investigates applying closed-loop audio feedback techniques to the creation of musical robots to equip them with new expressive capabilities, interactive applications, musical accuracy, and greater autonomy. In order to realise these objectives, following an investigation of the history of musical automata and musical robotic control systems, several new robotic musical instruments are developed based on the principals of utilising embedded musical information retrieval techniques to allow the instruments to continuously ‘listen’ to themselves while they play. The mechanical and electronic systems and firmware of a closed-loop glockenspiel, a modular unpitched percussion control system, and a robotic chordophone control system are described in detail, utilising new software and hardware created to be accessible to electronic artists. The novel capabilities of the instruments are demonstrated both through quantitative evaluations of the performance of their subsystems, and through composing original musical works specifically for the instruments. This paradigm shift in musical robotic construction paves the way for a new class of robots that are intuitive to use, highly accurate and reliable, and possess a unique level of musical expressiveness.