We consider a second output of the gestural interface, one that groups what can be called primary feedback [2] to the performer. The elements that form the primary feedback, in the case of hand gestures, are the tactile, kinaesthetic and proprioceptive feedback [4], the visual feedback and the primary auditory feedback (the keys sounds from a clarinet, for example), usually masked by the secondary auditory feedback, the actual sound produced by the instrument. (See later on this document for explanations on these topics)
A third output may exist, in the case of a force feedback [4]. It is essentially a type of kinesthetic feedback, but dependent on the current status of the sound production unit. There is here a serious question for virtual musical instrument designers: studies have shown 1 that force (and tactile) feedback and are important clues for the skilled performer (or expert performer) when playing an acoustic instrument (in opposition to the beginner that tends, according to these same studies, to strongly rely on visual feedback clues). This can be represented as sympathetic vibrations when playing a clarinet, the vibration sensed by the violin player on his shoulders and on the bow, etc. But if one plays an electronic saxophone controller (WX7, for example) or an electronic model of a violin, it is hard to reproduce the same effects as in the case of acoustic instruments. The solution calls for the use of actuators that simulate this behaviour.
One example of a virtual instrument that takes into account force feedback is the "clavier modulaire rétroactif" developed at ACROE - Grenoble, where electrical motors are able to produce a reaction equivalent to the gesture applied by the performer. [4]
But in order to discuss the gestural interface in more detail, we suggest that one may first consider the movement or gesture to be captured. Implementation of gesture controllers include different aspects related to gesture context and function, technologies, costs and other different interface design topics [5].
Let's now review and comment some works about gestures and try to establish
some simple definitions.