Development and Evaluation of a Hybrid Wind Instrument

A hybrid wind instrument generates self-sustained sounds via a real-time interaction between a computed excitation model (such as the physical model of human lips interacting with a mouthpiece) and a real acoustic resonator. Attempts to produce a hybrid instrument have so far fallen short, in terms of both the accuracy and the variation in the sound produced. The principal reason for the failings of previous hybrid instruments is the actuator which, controlled by the excitation model, introduces a fluctuating component into the air flow injected into the resonator. In the present thesis, the possibility of using a loudspeaker to supply the calculated excitation signal is evaluated; the loudspeaker is placed at the entrance of the resonator (a clarinet-like tube), along with a microphone. This work focusses particularly on two possibilities: using the instrument as a new musical instrument and using it as a tool to carry out wind instrument research. First, a theoretical study facilitates the modelling of the loudspeaker-resonator system and the design of a feedback and feedforward filter to successfully compensate for the presence of the loudspeaker. The prototype is then evaluated using physical models of a single-reed, a lip-reed and a bow-string interaction and using a purely mathematical “polynomial” excitation model. For the design of excitation models, the usefulness of dimensionless and reduced parameter forms is outlined, and a sound prediction theory is presented, enabling the pre-estimation of both amplitude and spectral related features of the self-sustained sounds. The resulting self-sustained sounds are evaluated by a mapping of their sound descriptors to the input parameters of the excitation models, both for sustained and attack sounds. For all excitation models, the sounds produced by the hybrid instrument are shown to match those predicted by simulation. However, the hybrid instrument is more easily destabilised for certain extreme parameter states

Physically-based modelling techniques for sound and synthesis

Among the many physically-based modelling techniques, various have been designed in computer music for sound synthesis. This text reviews some of the most important

Two-polarisation physical model of bowed strings with nonlinear contact and friction forces, and application to gesture-based sound synthesis

Recent bowed string sound synthesis has relied on physical modelling techniques; the achievable realism and flexibility of gestural control are appealing, and the heavier computational cost becomes less significant as technology improves. A bowed string sound synthesis algorithm is designed, by simulating two-polarisation string motion, discretising the partial differential equations governing the string’s behaviour with the finite difference method. A globally energy balanced scheme is used, as a guarantee of numerical stability under highly nonlinear conditions. In one polarisation, a nonlinear contact model is used for the normal forces exerted by the dynamic bow hair, left hand fingers, and fingerboard. In the other polarisation, a force-velocity friction curve is used for the resulting tangential forces. The scheme update requires the solution of two nonlinear vector equations. The dynamic input parameters allow for simulating a wide range of gestures; some typical bow and left hand gestures are presented, along with synthetic sound and video demonstrations