ï~~to re-empower not only the performer and the performing environment, but by extension also the listener. The intention was to build musical presence into the structure of production, by contrast with the pre-accreditation which we tend to demand ( risking by not risking ).One could then construct situations - compositions - the performer's knowledge of which could develop infinitely, and in a way organic to his own musical personality, without there being any question of "mastering" the work. This is what happens ideally in any musical situation, of course, but our tendency to fix and counterfeit has become so prevalent that it seems useful to design such habits out of a system of musical production. As far as possible, this is implemented without compromising the richness of the instrument and its technique, or adding extraneous techniques for the performer - most of the actions already form part of conventional performance. In keeping with this idea, it proved possible for the trumpet at the heart of the system to remain inviolate, thanks to the delicate and inventive work of the designer and builder of the electronics, Bert Bongers of Den Haag. The system described here was developed concurrently with the piece "Mirror-Rite" (Impett, 1994 ). All of the output, including soundprocessing, is calculated in real time from performance data. The output devices - sampling machine, synthesisers, processors and digital mixing - are all controlled by the system via MIDI. The instrument is also currently being used in the integrated environment of the IRCAM Signal Processing Workstation [Impett, 1993]. 3 Performance Parameters The position of the trumpet is read constantly in a 2m2 2-dimensional screen ( a third dimension is to be added), by ultrasound receivers below and to the side of the performer. A cluster of transmitters is attached to the bell of the trumpet, so as to be almost omnidirectional. Combined with timing information, this data produces a vector describing direction and speed of movement. A choreography of virtual instruments and processes can be constructed Within the resultant space. Information about the player's physical contact with the trumpet is provided by pressure sensors and mercury switches.Two pressure sensors are mounted on the right of the third valve casing, where ordinarily lie the only two fingers not engaged in moving valves or slides, or in supporting the trumpet. Below the centre of the bell there are two mercury switches, together providing a 4-stage value for the left-to-right inclination of the instrument. The three valves each contain a shielded magnet inserted into the cavity at the bottom of the piston. Their fields are read by corresponding sensors fitted in specially built extended lower valve caps. The valve positions can be used by the player as controllers, or interpreted as parameters abstracted from the act of performance, and provide a means of cross-checking pitch conversion. Breath pressure seemed instinctively an essential parameter to use: physically and musically the most direct, and simple to measure in technical terms. In fact what had appeared intuitively quite clear, and is without doubt central to the instrument, proved more difficult to quantify. Inserting a closed tube or balloon ( the usual ways of measuring breath pressure) is obviously out of the question. Both within the instrument and inside the player's mouth, the pressure - quite normal in the iirst case and very high in the latter - varies very little with volume, but changes in a more complex relationship with tessitura. In any case it was impossible to measure breath pressure or speed without compromising either playing technique or the acoustic integrity of the instrument. Ultimately Interactive Performance 148 ICMC Proceedings 1994 0
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