The Hyperbow: A Precision Violin Interface Diana Young Media Lab, MIT email:diana@media. mit. edu Abstract This paper addresses the need to utilize precision measurement techniques in the the creation of new performance instruments and interfaces. Discussed within is the design and construction of a new violin interface, the Hyperbow, which serves as a first demonstration of how a violin bow might be made capable of measuring the most intricate aspects of violin technique-the subtle elements of physical gesture that immediately and directly impact the sound of the instrument while playing. In order to provide this insight into the subtleties of bow articulation, a sensing system has been integrated into a commercial carbon fiber bow to measure changes in position, acceleration, and the downward and lateral strains on the bow stick. These sensors were fashioned using an electromagnetic field sensing technique, commercial MEMS accelerometers, and foil strain gauges. The measurement techniques used in this work were found to be quite sensitive and yielded sensors that were easily controllable by a player using traditional right hand bowing technique. 1 Introduction Though a great deal of progress has been made in the fields of audio analysis and synthesis, and software tools for musicians continue to quickly increase, there is comparatively little advancement in the area of performance instrument design and development, especially for accomplished players. Certainly, there is a great need for the development of new musical interfaces that may respond to the smallest and most subtle gesture of an accomplished musician. Not only may much be learned from accessing this level of description of musical technique, but by using this data we may begin to delve into new kinds of musical expression, building upon traditional methods of manipulating sound. Of course, care must be taken not to reduce the playability of the instrument in the development of such an interface. As in the study of a violin bow interface described here, when beginning with a traditional acoustic instrument as a model, this issue is of extreme importance. The violin (and its accompanying bow) is a prime candidate for study and evolution. Traditional violin repertoire and technique require extremely subtle articulations and sophisticated coordination of gesture, most of which is not easily understood by non-players. For these reasons, the violin is a source of inspiration for new music controllers. The problem of how to develop a new musical interface for an experienced string player in order to create new methods of musical expression was addressed in the Hypercello and subsequent Hyperinstruments work at the M.I.T. Media Lab (Paradiso and Gershenfeld 1997; Machover 1992). Later, projects such as the bossa (Princeton) were developed (Trueman and Cook 1999). These endeavors used measurements such as bow position, pressure on the bow stick, and acceleration of the bow to alter the sound produced by the bowed string. The Hyperbow project discussed in this paper is a music controller similar to those mentioned above, as the sensing system on which the controller is based includes sensors for bow position and acceleration (Young 2001). However, in order to provide greater insight into the subtlety of gesture demanded of and used by violinists, different types of strain in the bow stick are also measured. The downward and lateral strains on the bow stick are closely related both to the experience of a violinist while playing and to the immediate changes in the sound produced by the string when bowed. The three sensing subsystems-position, acceleration, and strain-were grafted onto a carbon fiber bow to enable (directly or indirectly) the Hyperbow to collect and transmit data reflecting bow position, speed, acceleration, downward force, and angle of the bow. This paper describes the implementation and design considerations of the Hyperbow project, applications, and future advancements. 2 Design and Implementation of the Hyperbow 2.1 Position Sensing The method of sensing the position of the bow (relative to the bridge of the violin) presented in this paper is an adaptation of the system used in the development of the Hypercello (Paradiso and Gershenfeld 1997). In this method, two square wave signals of different frequencies are produced. The signals are connected to opposite ends of a resistive strip that spans the length of the bow. A simple electrode antenna is placed behind the bridge of the violin. This antenna is connected 489
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