This ongoing work was supported in 2016-17 by a grant from the John S. and James L. Knight Foundation's arts program, which aims to engage and enrich Philadelphia through the arts. Philadelphia musician, music producer, and film maker Peter English worked in close collaboration with MET-lab researcher Jeff Gregorio to develop augmented instruments for use in a live music performance held in June 2017. Future development and exhibition in music performance and interactive sound installation are expected.
Preliminary work has focused on using acoustic synthesis methods to augment the sound production of acoustic drums. The system uses electromagnet actuators capable of inducing drum heads to vibration using both synthesized signals and modulated feedback taken from the drum. The system uses a power amplifier designed by former MET-lab researcher Dr. Andrew McPherson , and incorporates a custom preamplifier, signal processing on a Teensy 3.6 microcontroller, and inter-instrument communication on an ESP8266 wifi-enabled microcontroller. Schematics, board layouts, and firmware are available at https://github.com/JeffGregorio/ActuatedDrums.
We are currently working on incorporating a custom capacitive proximity sensing module for theremin-style interaction directly at the drum hoop. The following video shows an early prototype using a Doepfer A-178 Theremin Control Voltage Source module with the metal hoop serving as the antenna. This control is mapped to the feedback loop gain. We can see from this basic demonstration that we can use feedback to produce frequency beating effects, and that varying strike position at the drum head can excite different resonant modes of the drum.
The system also uses variable phase modulation of the feedback signal, implemented digitally as a simple interpolated delay line. Varying the phase delay can produce timbral modulations and effects, including reinforcement and suppression of the fundamental and other harmonic partials, as well as strong frequency beats. The following video shows a network of eight drums being driven with a 25/75 mixture of a synthesized sine wave and feedback while the phase delay is swept through 0-80ms.
Wireless communication to and between multiple drums in a network is implemented on the ESP8266-01 microcontroller using the Open Sound Control (OSC) protocol. This allows the drums to be played in the manner of a spatially-distributed polyphonic synthesizer by instructing the drums to synthesize arbitrary pitches. It also allows the drums to communicate amongst themselves by passing 'propagation' messages. Configuration of this behavior is facilitated by a central controller application written for OS X, which assigns 'listeners' to each drum. On certain conditions such as the falling edge of an amplitude envelope, each drum passes a propagation message to its listener(s). Propagation rate is affected by the amplitude envelope times, and duration is controlled by a propagation decay time variable. This behavior is shown in the following videos, on the first and second prototypes, respectively.
A network of sixteen actuated drums was used in a performance in June 2017 at Drexel University. The following video shows one song from the performance, recorded at a rehearsal session, in which the drums are configured to play harmony notes in response to the saxophonist.
 Andrew McPherson. 2012. Techniques and Circuits for Electromagnetic Instrument Actuation. In Proceedings of the International Conference on New Interfaces for Musical Expression. University of Michigan, Ann Arbor, Michigan.