Robotized artificial mouth for brass instruments: automated experiments and cartography of playing parameters
Résumé
In simple models of brass instruments (trumpet, trombone, etc.), important control parameters include the pressure in the mouth, the force applied by the mouthpiece on the lips and parameters which characterize the lips such as equivalent masses, dampers and stiffnesses (this is usually called the "mask" of the performer). It is easy to measure the pressure in the mouth during performance but not to access to other control parameters. This problem is similar for the voice (and multiplemass models of vocalfolds): in this case, the oscillating exciter becomes the vocalfolds rather than the lips and the resonator is the vocal tract rather than the trumpet. In order to have a reproducible and controllable experimental tool, the automation of an artificial mouth dedicated to the playing of brass instruments was made at IRCAM in the project of the National Research Agency CONSONNES (2005/2009, http://www.consonnes.cnrsmrs.fr), with the assistance of the Ecole des Mines de Paris, and BTS students. The actuators of the robot are: (A1) a solenoid valve controlling the air supply, (A2) a moving coil which allows to translate the artificial mouth and to monitor the lips force applied to the mouthpiece, (A3-4) two actuators controlling the volume water in each of the lips (latex chambers filled of water). The sensors used for measurements are: (S1-2) high precision pressure sensors (one in the mouth, one in the mouthpiece), (S3) an optical sensor measuring the opening between the lips, (S4) a force sensor (lipsmouthpiece), (S5-6) water pressure sensors (one in each lip). A few additional sensors are used for base controls (position sensors (S2bis-S4bis) of actuators (A2-4)) and to check experimental conditions (temperature and high pressure sensor for the air supply). Preliminary results and confrontations between theoretical models and experimental data has yet been obtained in [1,2] using this tool and a similar more advanced work has been performed on the clarinet in [3]. In this presentation, the current features of the robotized artificial mouth will be presented. First, basic mappings between the position of actuators (A2-4) and force or pressure signals (S45) are analyzed. This is used to calibrate the lips and to configure the machine as a testbed. Second, slowly timevarying commands are used to monitor the lips and to obtain sounds and quasistationary regimes. This makes appear various kind of regimes (non oscillating, quasiperiodic, nonperiodic, etc). Third, a sound analysis is processed to generate cartographies of sound descriptors such as energy, fundamental frequency (if any), sound ruggedness (etc) with respect to the quasi-static commands. This exploratory tool can be used to perform simplified and systematic analysis such as in [4]. Finally, although measures highlight hysteresis phenomena, the (complex) cartographies of regimes are sufficient to build some basic melodies (similar to those played by a novice unskilled players) during which all the signals of sensors (S1-6) can be recorded and analyzed. One possible evolution of such an exploratory tool could consists of adapting the mechatronics instruments to the case of artificial vocal folds and vocal tracts.