Radio Drum

Gesture-Sensing for Musical Performance: A Percussive Interface

GOAL

To create the next-generation Radio Drum. Note that ultimately it might not be a "Radio" Drum. The technology might end up being different. It must be a 3-dimensional controller that "doubles" as a drum. That is, it senses the space above a surface, but it also can be played like a drum, and identify "whacks" and different kinds of gestures, bounces, etc. It is a controller, and does not generate sound.

BACKGROUND

The fist-generation Radio Drum was designed by Bob Boie and built at Bell Labs in the mid-1980's as a "three-dimensional mouse." The Radio Drum uses capactive sensing; you use a radio frequency to measure capacitance. The two sticks are differentiated by using different frequencies for each one.

The Radio Drum itself could be called a "gesture sensor" that keeps constant track of the 3-dimensional spatial location of mallets in the following way: A small amount of wire is wrapped around the end of each of two sticks and acts as a conducting surface electrically driven by a radio frequency voltage source. The drum surface beneath the sticks receives the signal, and the x and y positions of the sticks are derived by determining the first moment of capacitance between the sticks and the surface below. The z position (height) is given by the reciprocal of the first moment. The greatest accuracy in z is in the region from about 5 cm above the surface and closer. The response time is between 5 and 10 msecs, but this latency can be lowered to below 5 msec. (For technical details see [Boie, et al 1989]).

WHAT WE HAVE

We have several copies of the original Boie drum (in fact we have all of them still in existence), and we have a design for a "wireless" version in progress. The new prototype wireless sticks were made last year by some UVic engineering grad students, and I think we can finish at least a basic prototype of the wireless drum by the end of 1999. Then we can test it and see if it is good enough. If not, we might use another technology, or possibly use a hybrid -- for example, one sensor method for "whack" and one for "continuous" modes.

SPECIFICATIONS

Temporal resolution: 1 millisecond latency

Spatial resolution: 1 millimeter resolution in x,y,z

1. Drum must be linear in x and y as much as possible. Or if not linear, at least well-behaved (i.e. not random) so that software can compensate for the nonlinearities.
2. Greater range of z if possible (more space above surface usable, up to a meter or more would be great).
3. Need to have edge effects under control (or have a boundary so you don't run into them).
4. There should be little or no "interference" between sticks (Max's drum definitely has this problem -- when the sticks are close together, they get less dependable).
5. ELIMINATE "DUFFING," that is, when a hard stroke or "accent" is reported as a soft one. Boie thinks this might be an actual physical phenomenon in which the material itself is distorting and sending electrical signals. I'm 99% sure this is a hardware problem. It is one of the things that makes the current drum frustrating to play.

IDEAS

1. Gesture detection (figuring out when you hit the drum) can be done by detecting a change of direction of the stick, and can be much more elegant than it is now. This is more like a real drum than the "threshold crossing" that Max's drum uses. But velocity might be better measured directly (the actual speed of the stick) rather than by reporting dz at the moment of change of direction, as it is done now. This would free us from constraints about what kind of foam we're using, which would make it more versatile. Velocity could be reported even if you're using a hard rubber surface that doesn't compress at all. Note that this can all be done on the host, even using MSP or other DSP tools to analyze the data stream, so again, we don't need to decide in advance. In fact, algorithms for gesture-detection can be an on-going process.
2. Should be able to put different kinds of stuff on the surface of the drum and then recalibrate the drum to work with that surface. We could provide people with some options, but they could also use anything they came up with too.
3. Would be nice to be able to see how the drum is configured right on its own surface; since this is a playing surface, it can't be an LCD, would probably have to use some kind of projection system.

REFERENCES

CNMAT's work on gesture sensing and interfacing (i.e. ethernet and/or XLR connections?). Is there any instrument made today that is ethernet yet? http://cnmat.CNMAT.Berkeley.EDU/OpenSoundControl/
MIT Media Lab -- Neil Gershenfeld (now working w/ the Flying Karamozov Brothers on a new show, using accelerometers on the clubs). He's got all kinds of tricks; if we find that the capacitance method isn't good enough, we should meet w/ him to see a panorama of possibilities. http://www.media.mit.edu/physics/
Tactex Controls -- "Smart fabric" technology for drum surface? (If using a hybrid system). This would be good for hands or sticks. www.tactex.com. This company is in Victoria and is very friendly. http://www.tactex.com./
Interface 1993: Intelligent Musical Instruments: The Future of Musical Performance or the Demise of the Performer
CMJ 1994: The Computer-Extended Ensemble
ICMC1990/Glasgow proceedings: Recent Advances in the Coupling of the Language Max with the Mathews/Boie Radio Drum
UCSD Symposium/1999: Improvising Across Borders in Cuba
ICMC 1994/Aarhus: A Virtual Piano Concerto -- The coupling of the Mathews/Boie Radio Drum and Yamaha Disklavier Grand Piano in "The Seven Wonders of the Ancient World."
Virtual Percussion: Drumming in the Ether. Invited lecture/concert with Mark Goldstein, IBM Research Headquarters, Yorktown Heights, New York, June 23, 1997.
Letter to Tatsuya Kitsuda, Yamaha Corporation, about building a new drum.
Pisa, Italy: Man-Machine Interaction in a Jazz Improvisation Context, presented at First International Workshop on Man-Machine Interaction in Live Performance.
ICMC 1989/Ohio State proceedings: The Radio Drum as a Synthesizer Controller. By Max Mathews and W. Andrew Schloss.
Strumenti Musicali (Italian music magazine, Torino Italy): Andy Schloss e il Radio Drum (interview conducted by Giovanni Ramello).

VIDEOS THAT SHOW THE RADIO DRUM IN CONCERT:

Western Front: Suite from the Seven Wonders
ONADIME demo with live images generated from the drum along with the Suite
MS/NBC news show with live piano demo
Wildlife performance from Stanford's Centennial concert with DAJ
UCSD video of live performance of first four movements of Seven Wonders
Middle East/ MIT concert in Boston, May 1999 (not great audio quality)

written by Dr. A. Schloss, School of Music, UVic, aschloss@finearts.uvic.ca