Análise acústica e cinemática da técnica de mudança de posição no contrabaixo acústico

Abstract

This study investigates the position shifting technique on double bass from two complementary approaches: kinematic and acoustic analysis. Although the position shifting movement on double bass has been considered in this study as inherently complex and dependent on many factors (physiological, cultural and artistic), in this research, we based the kinematic analysis on ideas from a specific scientific field and considered only one dimension of the phenomenon. We have suggested that, to some extent, due to its demand for speed and precision, the position shifting is similar to the category of goal directed aiming movement, developed and studied in Motor Behavior. We aimed to evaluate the technique of position shifting using the two-component model of goal-directed aiming by WOODWORTH (1899), which assumes a certain level of central control and divide the movement into two components: a first phase, derived from central processing and a second phase that depends on some sort of feedback and online control. In later developments of the model, it was found that movement variables such as amplitude and direction influence its characteristics. The study included five bassists with varying levels of experience who performed excerpts from the traditional repertoire of the instrument. The performances were captured through audio recording and motion capture. The position shift was then evaluated in four different conditions, corresponding to variations in the amplitude and direction of movement: 1) short, ascending; 2) short, descending; 3) long, ascending and 4) long, descending. This study sought to evaluate the influence of these conditions and also the level of experience in the movements of individuals. To carry out the analysis of the information collected, we developed acoustic and kinematic descriptors through which the subjects performances could be measured and compared. As acoustic descriptors, we used articulation index and spectral flux. As kinematic descriptors, we used the motion total duration, speed peak, proportion length of the first phase and discontinuities in acceleration curve.Based on analysis of those descriptors, it was found in this study that the subject's experience influences the acoustic and kinematic characteristics of its position shifting technique. It was found that the evaluated conditions also influence the characteristics of the position change, although it was not possible to determine how this influence occurs.