Paramètres physiques d'un oscillateur changés par contrôle actif. Application à la lame de xylophone

International audienceOn the input admittance of many violins a typical broad frequency peak, called "bridge hill" appears around 2.5 kHz. The physical parameters of a violin bridge have a significant influence on this feature, and then on the tonal colouration of the produced sound. The effect of the bridge characteristics (mass, stiffness and foot spacing) on the frequency response have been revealed by using bridge models through several studies. Here the parameters of the bridge response are changed, by applying an active control method. Such a correction, very useful in noise reduction, enables to change separately the position and the shape of the bridge hill. It is first tested on a simplified bridge model, then on a real bridge by placing 2 actuators and an accelerometer at strategic positions

THE ACOUSTICS OF THE TROMBONE : HOW DO PLAYERS LIP UP AND DOWN?

International audienceFour advanced trombonists and three beginners played the note B ♭2 (the lowest normal note played with the slide retracted), then 'lipped up and down'. The normal playing frequency lies above that of the bore impedance peak, so the bore is a compliant load. However, the range reached while lipping is approximately centered on this peak. To investigate how the lip oscillation is regenerated with inertive or compliant acoustic loads, acoustic pressure and flow waveforms were determined both up-and downstream from the lips, while playing. The lip opening area and the flow component due to the lips' sweeping motion were also estimated using a transparent mouthpiece and high-speed video. The lips move forward before separating, then backward before closing. Consequently, the acoustic flow into the mouthpiece becomes positive before the lips open. Further, the volume V of air swept by the lips in the direction of the flow is positive around one cycle. A model in which the lips execute out-of-phase simple harmonic motions in the forwards and vertical directions is consistent with the results. The pressure difference Δ across the lips does nett positive Δ work on the lips, providing sufficient energy for regeneration of the oscillation. As the note is lipped down to inertive load, the phase of the mouthpiece pressure moves ahead of that of the flow, and Δ moves further ahead of the volume of air swept in the horizontal direction. The latter effect decreases Δ work, so, for very inertive loads, the oscillation stops. Lipping upwards is limited partly because negative mouthpiece pressure must always overlap largely with the lips being closed, and the limited magnitude of sweeping flow limits the extent to which flow can lead the lip aperture. Consequently, further increases in lip stiffness produce jumps to the next impedance peak

Méthodes de contrôle actif d'instruments de musique. Cas de la lame de xylophone et du violon.

In Musical Acoustics, modal control is commonly used to modify the vibration characteristics of musical instruments.The number of transducers used to control the structures of such systems is typically reduced. In addition, their mechanical properties and their localization are optimized, so that they do not disturb the vibration of the instrument nor the musician playing.In this thesis, we suggest a control method adapted to these constraints. It allows modifying the characteristics of the resonance peaks in the frequency response of the plant. This is achieved using a single sensor and the calculation of the actuator signal is based on the measurement itprovides.We apply the suggested method to a xylophone bar of which the mechanical properties are suitable for active control, and to a good quality violin made in a traditional way. For both instruments, we succeed to modify the frequency and the maximum gain of their resonances.Through the experiments carried out in the thesis, we use the modal control method in order to allocate the desired characteristics to the radiated sound of the musical instruments.Furthermore this method is suitable to study the relationship between the frequency responsesand the mechanical properties of the instruments.En acoustique musicale, la technique du contrôle actif est utilisée pour modifier les caractéristiques de vibration des instruments de musique.Pour de tels systèmes, le nombre de transducteurs utilisés est souvent réduit. De plus, leurs propriétés mécaniques et leurs positions sont optimisées de façon à ne pas perturber la vibration de l’instrument, ni le jeu du musicien.Nous proposons dans cette thèse une méthode de commande adaptée à ces contraintes. Elle permet de changer les caractéristiques des pics de résonance de la réponse fréquentielle du système. Pour cela, elle nécessite un seul capteur et calcule le signal des actionneurs uniquement à partir de la mesure qu’il fournit.La méthode proposée est appliquée à une lame de xylophone dont les propriétés mécaniques sont adaptées au contrôle actif, puis à un violon de bonne qualité fabriqué par un luthier. Dans les deux cas, elle parvient à modifier la fréquence et le gain maximal de leurs résonances.À travers ces expérimentations, la méthode de commande modale apparaît comme une technique capable d’attribuer les caractéristiques souhaitées au son rayonné par les instruments de musique. D’autre part, elle constitue un outil adapté pour étudier la relation entre leurs réponsesfréquentielles et leurs propriétés mécaniques

Treating bibliometric indicators with caution: their dependence on the source database

International audienceNowadays, with computer-supported analysis of databases, constructing bibliometric or scientometric indicators may be considered easy. The problem is more to verify the accuracy of the global analysis, including the sampling of data. The global coherence of an analysis depends on the adequacy of all the steps. Using on-line databases, an experiment was designed to demonstrate this. Keeping the same protocol for data collection, the same indicators are used over the various samples . The results from three separate databases are profoundly different.Aujourd'hui, avec l'analyse automatique des bases de données, la construction d'indicateurs bibliométriques ou scientométriques est facilitée. Le problème est plus de vérifier l'exactitude de l'analyse globale, y compris l'échantillonnage des données. La cohérence globale de l'analyse dépend de la pertinence de tous les maillons de la chaîne. En utilisant des bases de données en ligne, une expérience a été conduite : les mêmes indicateurs ont été utilisés sur différents échantillons. Les résultats obtenus sont profondément différentes

Relations entre pression, débit, mouvement ds lèvres, et impédances amont et aval pour le trombone

International audienceThis experimental study investigates ten subjects playing the trombone in the lower and mid-high range of the instrument, B[2 to F4. Several techniques are combined to show the pressures and the impedance spectra upstream and downstream of the lips, the acoustic and total flows into the instrument , the component of the acoustic flow due to the sweeping motion of the lips, and high speed video images of the lip motion and aperture. The waveforms confirm that the inertance of the air in the channel between the lips is usually negligible. For lower notes, the flow caused by the sweeping motion of the lips contributes substantially to the total flow into the mouthpiece. The phase relations among the waveforms are qualitatively similar across the range studied, with no discontinuous behavior. The players normally played at frequencies about 1.1% above that of the impedance peak of the bore, but could play below as well as above this frequency and bend from above to below without discontinuity. The observed lip motion is consistent with two-degree-of-freedom models having varying effective lengths. These provide insight into why lips can auto-oscillate with an inertive or compliant load, or without a downstream resonator

SONIFICATION OF PHYLOGENETIC TREES: LISTENING TO EVOLUTION

International audienceA phylogenetic tree is a visual representation of the evolutionary relationships linking organisms or species, analogous to a genealogy for members of a family. In phylogenetic trees, nodes represent ancestors, leaves represent species, and edges represent time or the amount of character or genetic change. The visualization and the comparison of such hierarchical structure can be very challenging, especially when the number of species is high. In this work, we suggest a new approach for getting insights into the main structural features of phylogenetic trees. We define simple rules for the sonification of a phylogeny and apply them to the simplified tree of Boroeutheria, a group of mammals comprising, among others, human, mouse, rabbit, whale and cat. This approach appears to be very promising for better apprehending tree structures

Analog circuits and Port-Hamiltonian realizability issues: a resolution method for simulations via equivalent components

International audienceIn order to simulate the Ondes Martenot, a classic electronic musical instrument, we aim to model its circuit using Port-Hamiltonian Systems (PHS). PHS have proven to be a powerful formalism to provide models of analog electronic circuits for audio applications, as they guarantee the stability of simulations, even in the case of non-linear systems. However, some systems cannot be converted directly into PHS because their architecture cause what are called realizability conflicts. The Ondes Martenot circuit is one of those systems. In this paper, a method is introduced to resolve such conflicts automatically: problematic components are replaced by equivalent components without altering the overall structure nor the content of the modeled physical system

Analog circuits and Port-Hamiltonian realizability issues: a resolution method for simulations via equivalent components

International audienceIn order to simulate the Ondes Martenot, a classic electronic musical instrument, we aim to model its circuit using Port-Hamiltonian Systems (PHS). PHS have proven to be a powerful formalism to provide models of analog electronic circuits for audio applications, as they guarantee the stability of simulations, even in the case of non-linear systems. However, some systems cannot be converted directly into PHS because their architecture cause what are called realizability conflicts. The Ondes Martenot circuit is one of those systems. In this paper, a method is introduced to resolve such conflicts automatically: problematic components are replaced by equivalent components without altering the overall structure nor the content of the modeled physical system

Comment l'état de surface du bois modifie les caractéristiques des résonances dans la perce des instruments à vent

Dans les registres bas et medium, la jouabilité des instruments à vent dépend des caractéristiques des résonances de la colonne d'air. Dans le cas des instruments en bois, ces caractéristiques sont liées à l'état de surface de la perce sur lequel le facteur et le musicien peuvent agir par le choix de l'essence, de la direction du fil de coupe et le huilage. Nous mesurons les impédances d'entrée de tuyaux en érable avec différents états de surface. L'application d'un bain d'huile accroît significativement les facteurs de qualité et amplitudes des douze premières résonances acoustiques de la perce. Lorsque le fil de coupe est de biais relativement à la direction du tronc, la porosité du tuyau est supérieure et l'effet d'un second bain d'huile sur ces caractéristiques est plus important. Les tuyaux dont le fil de coupe est droit et ayant subi deux bains d'huile ont une impédance d'entrée proche de celle d'un modèle de tuyau rigide