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CARACTERISATION OBJECTIVE DE LA QUALITE DE JUSTESSE, DE TIMBRE ET D'EMISSION DES INSTRUMENTS A VENT A ANCHE SIMPLE

Abstract : Two methods for characterising the acoustic features (pitch, timber, easiness of playing) of single reed woodwind instruments are developed and tested. On one hand, we study the resonator, and on the other hand we make a numerical simulation of the auto-oscillations resulting from the coupling between the resonator (supposed linear) and the excitator (supposed to be a non linearity at the mouthpiece input). The studied physical variables are the fundamental frequency and the spectrum of the pressure in the mouthpiece. In all the study, these variables represent respectively the pitch and the timber. In order to test the two methods, we compare these variables with variables measured in the mouthpiece of real instruments. These are played with the help of a blowing machine that we built to reproduce the musician embouchure accurately. We begin with a historical background and choose a physical model. The analysis of the solutions resulting from the model enables to show that the fundamental frequency can be deduced from resonance frequencies for the linear threshold. This is possible by means of a corrective term, called the length correction. This term represents the effect of the embouchure and does not depend on the frequency. The discrete solutions of the model are calculated with the help of the measured input impedance and embouchure characteristics. We choose the sampling frequency values with respect to the resonator input impedance. This enables to minimise numerical errors on the discrete reflection function. Since the simulation uses measured input impedance, sampling frequency values are small with respect to the reed resonance frequency. We chose the compensated bilinear transformation which gives a "discrete" reed whose properties are near from those of the "analog" reed. Input impedance and fundamental frequencies of the pressure in mouthpiece are measured for all the fingerings of the two first registers of a clarinet and an alto saxophone. The resonance frequencies and the fundamental frequencies are compared for each fingering. For each register, we evaluate a length correction, due to the embouchure. Comparisons between measured and calculated pressures in a clarinet mouthpiece for some fingerings show that the simulation detects "difficult fingerings" if low blowing pressures are used in the model. The bending of the reed against the curved lay of the mouthpiece is not taken into account in the model and seems to be the major reason for this discrepancy. A first theoretical approach of this mechanical phenomenon is proposed in appendix A.
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  • HAL Id : tel-00854901, version 1

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Bruno Gazengel. CARACTERISATION OBJECTIVE DE LA QUALITE DE JUSTESSE, DE TIMBRE ET D'EMISSION DES INSTRUMENTS A VENT A ANCHE SIMPLE. Acoustique [physics.class-ph]. Université du Maine, 1994. Français. ⟨tel-00854901⟩

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