REAL-TIME CONTROLLERS FOR PHYSICAL MODELS
Chris Chafe Associate Professor of Music
Perry R. Cook Research Associate
The computational reductions brought about by new work in algorithms such as the Waveguide filter formulations, along with improvements in DSP chips and other signal processing hardware, have made possible the real-time synthesis of music by physical modeling. Such instruments require new modes and levels of control. Work in increasing the bandwidth of synthesizer control by exploiting all available degrees of freedom has yielded a number of experimental hybrid controllers (Cook, Chafe). Controllers based on the paradigms of wind and stringed instruments have improved the control of models based on these families, and research is being conducted to create a more general controller which is not constrained to a particular family of instruments.
Mapping physical gestures to a DSP synthesis controller is being studied by experimentation. Early studies in simulation (Chafe, 1985) suggested that linear mappings are not the way to go. The current development system allows trial-by-feel investigation of alternative scalings.
The area of tactile feedback (Chafe) is being investigated, as this is an important area of control for the traditional instrument player. Initial trials have begun using actuators feeding audio to the touch point. A general preference has been shown with the technique. The next stage will be to quantify what enhancement, if any, results from feeling the instrument's vibrations. Also, such considerations as tactile frequency bandwidth and vibrations characteristic of contact points will be studied.
New pieces are being written using real-time controllers and the DSP-based physical models. "El Zorro'' is a recent composition by Chris Chafe that employs a Lightning Controller (by Buchla and Associates). The soloist is steering note-generation algorithms in terms of tempo, tessitura and "riff-type.'' Gesture and position is tracked with the Lightning's infra-red controllers. Some direct control is exercised over DSP effects via MIDI. A composition project in the works uses the Celletto (an electronic cello) to interact with the DSP synthesis at the control level. The cellist will evoke synthesis related to natural cello behavior directly from the instrument. For example, bow speed might translate into breath pressure control of a wind synthesis.