Investigating cello sound production beyond ordinary bowing

Music acoustics is the discipline that studies the function of music instruments. During the last century, numerous studies have analysed the production of sounds, the vibrations of several parts of the instruments and the manner instruments transmit sound to the audience. The analysis of the playing techniques that musicians use to achieve different sounds has required new experimental methods and computer simulations in order to fully cover the wide range of sounds that instruments produce. In bowed string instruments, such as the violin or the cello, the friction that takes place at the position where the bow hairs touch the string is mainly responsible for the sound production. To achieve a bowed sound, players precisely control the speed and the force of the bow in order to produce a so-called stick-slip motion, where the bow sticks to the string during few milliseconds and then the string quickly slips back before the next cycle of oscillation begins. At least this is what is expected from an ordinary bowed-string sound. These instruments, though, can achieve a large variety of sound textures. For example, by adjusting the bowing pressure on the strings or by bowing on other parts of the instrument or even using the wooden part of the bow, composers and players have explored new sound effects giving birth to non- ordinary playing techniques. Such techniques challenge the way acoustics has defined the production of bowed-string sounds, showing the need for more systematic research. This project is dedicated to the study of non-ordinary bowing techniques on the cello. The main objective of the project is to analyse the bowing technique in cello performance while linking three experimental approaches. The first study will characterise the sound and movements of experienced cello players when they perform traditional and non-ordinary bowing techniques. To do that, motion-capture technology will record the movement of the bow during playing while sensors on the instrument will measure its vibration. Secondly, a robotic arm will be used in combination with sensors to create a fine-controlled bowing device where the bowing actions can be reproduced and analysed accurately. The third part of the project will be dedicated to evaluate the performance of the bowing device. This will consist of acoustical analyses of the recorded signals as well as listening tests where expert cello players will compare the sounds produced by players with those produced using the device. By combining these methodologies, the project will establish in which way every characteristic of the performed sounds depends on each of the player actions. This will result in a systematic description of the interactions between cellists and their instruments that will lead to a better understanding of the physics taking place during cello sound production.

The research project has systematically analysed cello sound production by considering ordinary and non-ordinary bowing techniques, using a multidisciplinary experimental approach. Its central achievement lies in the integration of three complementary experimental methodologies. First, the sound and bow movements of expert cellists were characterised using motion capture (3D motion recording), with a focus on both standard and extended bowing techniques. Second, a robotic arm was used as a bowing device to reproduce complex gestures mimicking the previously obtained motion capture recordings. Third, the perceptual aspects of extended bowing techniques were examined in terms of timbre analysis and the semantics used by experienced musicians. This approach provided systematic ways of linking specific bowing gestures with the resulting sounds, focusing on the reproducibility of the bowing motion, and the distinctive acoustic properties of the sounds produced. The purpose of the studies was to clarify how performer actions shape sound production beyond classical bowing techniques. Preliminary studies considered not only bow motion but also cellist posture and instrument positioning. Subsequent sound and motion analyses revealed novel timbral effects of extended techniques, such as col legno tratto, which involves using the wood of the bow on the strings. By combining motion capture data with robotic reproduction, the research project demonstrated a new framework for investigating bow actions. This framework enables the reproduction of bow movements with unprecedented realism and repeatability. The project shows that the acoustics of the cello, particularly in relation to non-ordinary performance practices, challenge existing methods for bowed string instruments. The results bring new insights into player-instrument interactions and our perception of non-conventional sounds. By showcasing the cello's expanded expressive sound palette, the research highlights the importance of further investigating non-ordinary playing techniques - a field that is continually being explored by composers and performers alike. Overall, the project provided valuable material for further work in performance science, musical acoustics, and acoustics education, emphasising the need for more interdisciplinary research connecting music and physics.