The Rulers is a self-contained musical performance system called a digital musical instrument . It includes a software component to produce music and a physical interface to manipulate it. Originally designed in 2004 by David Birnbaum as part of CCRMA’s Summer music technology seminar, it is currently undergoing an overhaul so that it is suitable to be played at the McGill’s Digital Orchestra. source: IDMIL webpage
The instrument was designed to evoke the gesture of plucking or striking a ruler that is fixed at one end. Because the seven aluminum beams are of various lengths, each beam oscillates for a different amount of time when plucked. This provides an element of visual and passive haptic feedback to the player. The design minimizes the acoustic component of the oscillations and vibrations of the beams. While they oscillate silently, their motion is sensed to control a computer-based synthesizer .
In the first versions of the instrument, the motion of each beam was measured using ordinary sensors such as infrared and Hall effect sensors. These sensors are relatively cheap, widely available, and simple to deploy. However, their metrological features are limiting, including non-linear behaviour and non-monoticity. In order to overcome these limitations, we introduced the use of strain gages and sensor fusion. The deployment of advanced signal processing techniques, specialized sensors, and sensor fusion proved to be effective on improving accuracy and instrument reliability. Besides that, the diverse physical principles of the different sensor technologies involved (infrared, Hall effect, and strain gages) allows for human motion classification, yielding richness and variety for composition and performance.
This work was published in SMC2011 conference  and in the IEEE Sensors Journal , where a novel framework for Kalman filter implementation is presented.
Pietro Verrecchia (while Electrical Engineering Undergraduate Student at McGill) contributed to this project, evaluating proximity sensors and developing analog electronic circuits.
opening photo: Xenia Pestova playing The Rulers | by: Vanessa Yaremchuk
remaining photos: CIRMMT Motion Capture Laboratory | by: Guillaume Pelletier
1. Carolina Brum Medeiros and Marcelo M. Wanderley. ”Evaluating of sensor technologies for The Rulers, a kalimba-like Digital Musical Instrument”. In Proceedings of the 8th Sound and Music Computing Conference, Padova, Italy, 2011.
2. M. M. Wanderley and P. Depalle, “Gestural control of sound synthesis,” Proc. IEEE, Spec. Issue on Eng. and Music – Supervisory Control and Auditory Communication, vol. 92, no. 4, pp. 632–644, 2004.
3. D. Levitin, S. McAdams, and R. Adams, “Control parameters for musical instruments: A foundation for new mappings of gesture to sound,” Organized Sound, vol. 7, no. 2, pp. 171-189, 2002.
4. Carolina B. Medeiros and Marcelo M. Wanderley. “Multiple-model Linear Kalman Filter Framework for Unpredictable Signals.” IEEE Sensors Journal, 2013, DOI 10.1109/JSEN.2013.2291683.