An interesting interface that began life in the 1980's as a percussion controller was computer music pioneer Max Mathews' "Daton", where a sensitive plate responded to the location and force of a strike. The strike location was determined by measuring differential force with 4 pressure sensors at the corner plate supports. Mathews then collaborated with his colleague at Bell Labs, Bob Boie, who evolved this device into one of the best known modern interfaces in academic music, the "Radio Baton". This instrument is played with two batons, one in each hand. The 3D location of each baton can be determined above a sensitive platform by measuring the signal induced through capacitive coupling between oscillators driving transmit electrodes in the batons and shaped receive electrodes in the platform.

A similar interface has been designed by Donald Buchla. Termed the "Lightning", this is an optical tracker that measures the horizontal and vertical positions of a pair wireless wands, each with a modulated IR LED at its tip. The current version of this system is specified to sense across a region 12 feet high by 20 feet wide. A highly-interpreted MIDI output stream can be produced, ranging from simple coordinate values through complicated responses to location changes, beats, and gesture detection. Other researchers have explored related optical interfaces; i.e. the Light Baton by Bertini and Carosi at the University of Pisa and the IR baton of Morita and colleagues at Waseda University both use a CCD camera and frame-grabber to track the 2D motion of a light source at the tip of a wand in real time.

A series of batons have been produced that sense directional beats via an array of accelerometers. These include 3-axis devices such as the baton built by Sawada and colleagues at Waseda University, the MIDI baton designed by David Keane and collaborators at Queens University in Kingston Canada, and a commercial dual-wand MIDI unit called the "Airdrum" made by Palmtree Instruments in 1987. Even simpler devices have been built with simple inertial switches replacing the accelerometers; these establish momentary contact when the baton velocity changes sign in the midst of a beat. Examples are the Casio SS1 Soundsticks and other such devices that have appeared on the toy market.

The "Digital Baton", which we have built at the MIT Media Lab, incorporates both of the sensor modes mentioned above; i.e., it tracks the horizontal/vertical position of an IR LED at the baton tip for precise pointing (using a synchronously demodulated PSD photosensor to avoid problems with latency and background light) and uses a 3-axis 5G accelerometer array for fast detection of directional beats and large gestures. It also features 5 force sensors potted in the urethane baton skin for measuring distributed finger/hand pressure. This multiplicity of sensors enables highly expressive control over electronic music; the performer can "conduct" the music at a high level, or descend into a "virtuoso" mode, actually controlling the details of particular sounds. We have used this baton in hundreds of performances of the Brain Opera at several worldwide venues.

From American Innovations in Electronic Musical Instruments
by Joseph A. Paradiso
© 1999 NewMusicBox