String Bowing Gestures at Varying Bow Stroke Frequencies: A Case Study

The understanding of different bowing strategies can provide key concepts for the modelling of music performance. We report here an exploratory study of bowing gestures for a viola player and a violin player in the case of bow strokes performed at different frequencies. Bow and arm movements as well as bow pressure on strings were measured respectively with a 3D optical motion capture system and a custom pressure sensor. While increasing bow stroke frequency, defined as the inverse time between two strokes, players did use different bowing movements as indicated from the measurement of bow velocity and arm joint angles. First, bow velocity profiles abruptly shift from a rectangle shape to a sinus shape. Second, while bow velocity is sinusoidal, an additional change is observed: the wrist and elbow relative phase shifts from out-of-phase to in-phase at the highest frequencies, indicating a possible change in the players coordinative pattern. We finally discuss the fact that only small differences are found in the sound while significant changes occur in the velocity / acceleration profiles.