Bowing virtual strings

A virtual string has been designed with the association of a sensor, a real-time algorithm and a mechanical actuator. The force exerted by a real bow on a small surface is measured, the velocity that a real string would exhibit under this excitation is computed by a fast DSP-board and the corresponding motion is generated by the actuator at the bowed surface. Corrections are needed for taking into account the characteristics of these various elements. They are achieved by means of IIR filters designed with LMS optimizations. One finally observes the classical Helmholtz motion of the bowed string, although some stability problems may still to be overcome.