Nicolas Lopes

Energy Balanced Model of a Jet Interacting With a Brass Player’s Lip

In most physical models of brass instruments, the air jet (located at the exciter) is governed by an equation of Bernoulli-type for which basic, unsteady or lossy versions are available. The non-linearity introduced by such model is known to be of utmost importance for wind instruments: it is responsible for self-oscillations when fed by a power source. However, this type of model is unable to make the air flow work at a mobile boundary (lip) as it does not account for any transverse component (the vertical dimension during normal brass playing) in the velocity field. In this sense, it is ill adapted to properly address the power exchanges between the jet and the lips. This paper addresses the following twofold issue. The first issue is the derivation of an air flow model in the unsteady case that restores the fundamental property of passivity at boundaries. The second issue is the test of its relevance in self-oscillating contexts, based on passive-guaranteed simulations of a simplified complete instrument. To make the air flow model as simple as possible, its derivation relies on standard Bernoulli assumptions (irrotational, incompressible flow without loss) except for the boundary conditions at the wall. It is derived in two steps. First, we solve the 2D velocity and pressure fields of the Euler equation for boundary conditions that are adapted to a moving lip. Second, we derive a macroscopic model based on averaged velocities and pressures. This yields a finite dimensional differential system which proves to be equivalent to the original one, in the sense that both the velocity and the pressure fields can be recovered from the macroscopic variables. Moreover, it preserves the power balance of the original physical system. Then, a simplified model of an instrument is built by connecting this system to a lip (mass-spring-damper) and to a conservative straight pipe with an ideally dissipative termination. Passivity is fulfilled and the complete power balance is explicitly encoded by recasting the model into the “Port-Hamiltonian formulation”. A numerical scheme that preserves passivity is proposed to simulate the complete system supplied by an ideal air pressure generator. Finally, results are compared with those based on the standard Bernoulli equation.

Simulating different upstream coupling conditions on an artificial trombone player system using an active sound control approach

Recent research suggests that the ability to finely tune vocal-tract resonances during trombone playing may constitute an important aspect of performance expertise. Artificial player systems, designed to reproduce the behaviour of a real player, often neglect this component by not providing any control of upstream resonances. However, they offer great experimental platforms for quantitative studies on sound production mechanisms, allowing independent adjustment of certain control parameters. An active sound control method was designed to improve high tone support and investigate different conditions of coupling between the artificial lips, the downstream air-column and the upstream cavity during sustained tones played by an artificial valve-trombone player system. Upstream input impedance at the fundamental frequency was controlled through real-time adjustment of the phase and amplitude ratio between the acoustic pressure generated on both sides of the lips. The phase difference between the upstream and d...

Open-loop control of a robotized artificial mouth for brass instruments

In order to have reproducible and controllable experiments, a robotized artificial mouth dedicated to brass instruments has been developed (CONSONNES project of the French National Research Agency). The actuators control: (A1) the airflow, (A2) the mouth position (monitoring the lips force applied to the mouthpiece), (A3-4) the water volume in each lip (water-filled latex chamber). The sensors measure: (S1-2) the pressure in the mouth and the mouthpiece, (S3: optical sensor) the area between the lips, (S4) the force lips/mouthpiece, (S5-6) the water pressure in each lip, and (S2bis-S4bis) the position of the moving coils (A2-4). We present an open-loop control obtained from measures, according to the following steps. First, a calibration for the lips control is performed, by analyzing signals (S4-6) w.r.t. positions (S2bis-S4bis), with no airflow. Second, slowly time-varying calibrated commands (A2-A4) are used to obtain quasi-stationary regimes (non oscillating, quasi-periodic, etc), for constant airflow...