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A comparison of single-reed and bowed-string excitations of a hybrid wind instrument

Buys, Kurijn; Sharp, David and Laney, Robin 

A hybrid wind instrument is constructed by connecting a theoretical excitation model (such as a real-time computed physical model of a single-reed mouthpiece) to a loudspeaker and a microphone which are placed at the entrance of a wind instrument resonator (a clarinet-like tube in our case). The successful construction of a hybrid wind instrument, and the evaluation with a single-reed physical model, has been demonstrated in previous work. In the present paper, inspired by the analogy between the principal oscillation mechanisms of wind instruments and bowed string instruments, we introduce the stick-slip mechanism of a bow-string interaction model (the hyperbolic model with absorbed torsional waves) to the hybrid wind instrument setup. Firstly, a dimensionless and reduced parameter form of this model is proposed, which reveals the (dis-)similarities with the single-reed model. Just as with the single-reed model, the hybrid sounds generated with the bow-string interaction model are close to the sounds predicted by a complete simulation of the instrument. However, the hybrid instrument is more easily destabilised for high bowing forces. The bow-string interaction model leads to the production of some raucous sounds (characteristic to bowed-string instruments, for low bowing speeds) which represents the main perceived timbral difference between it and the single reed model. Another apparent timbral difference is the odd/even harmonics ratio, which spans a larger range for the single-reed model. Nevertheless, for both models most sound descriptors are found within the same range for a (stable) variety of input parameters so that the differences in timbre remain relatively low. This is supported by the similarity of both excitation models and by empirical tests with other, more dynamical excitation models. Finally, a generalised stability condition for the hybrid instrument is obtained: the derivative of the dimensionless nonlinear function (which characterises the excitation model) should stay below unity over its entire operational domain.