Proceedings of the International Conference on New Interfaces for Musical Expression, Baton Rouge, LA, USA, May 31-June 3, 2015 Distributed Mechanical Actuation of Percussion Instruments Eric Sheffield Michael Gurevich University of Michigan University of Michigan Department of Performing Arts Technology Department of Performing Arts Technology School of Music, Theatre & Dance School of Music, Theatre & Dance Ann Arbor, Michigan Ann Arbor, Michigan [email protected] [email protected] ABSTRACT strings [12]. Similar electromagnetic systems have been applied to a This paper describes a system for interactive mechanically actuated Fender Rhodes [17], the electric guitar [15], and the vibraphone [3]. percussion. Design principles regarding seamless control and In the transducer-driven category are instruments like the Overtone retention of natural acoustic properties are established. Performance Fiddle [14] and the EMDrum [16]. It could be argued that these patterns on a preliminary version are examined, including the examples are in fact still electromagnetic in that they use voice coils potential for cooperative and distributed performance. as the excitation method, but a major distinction from purely electromagnetic systems is that the transducer is mechanically coupled to the instrument. In the Overtone Fiddle, this is done with a Author Keywords transducer attached to the body of a violin, while the EMDrum’s NIME, percussion, actuated instrument, augmented instrument transducer is coupled to the drum membranes using a rod that extends through the center of the moving coil. ACM Classification Perhaps a subset or extension of the electromagnetic and H.5.2 [Information Interfaces and Presentation] User Interfaces transducer-driven categories are feedback systems that can be used in J.5 [Arts and Humanities] Performing Arts conjunction with an input device, such as a contact mic, to create feedback loops at resonant frequencies. Processing, commonly in the form of bandpass filters, can be used within the loop to accentuate 1. INTRODUCTION specific harmonics. A popular guitar accessory, the Ebow, employs The recent proliferation of actuated acoustic instruments presents this technique, though it has also been applied to some of the intriguing potential for expanding the available gestures and timbres aforementioned actuated instruments, among others [e.g. 15, 16]. on instruments that already have an established performance practice Bowers and Haas’s “Hybrid Resonant Assemblages,” which share and repertoire. Since most implementations of actuation operate by some aesthetic characteristics with the world of multi-percussion in amplifying and reinforcing natural resonances in the instruments, the the use of found objects and performer-designed instruments, create world of non-pitched percussion has seen little development in this feedback loops with a fixed base and a malleable superstructure [4]. area; what does exist tends to focus on robotic musicianship. In this The properties of the feedback change as the performer manipulates paper, we present a non-robotic performance system of mechanical the tins, jars, boxes, Petri dishes, and other objects used as actuation that does not rely on acoustic resonance, thus opening the superstructure elements. door to any percussion instrument, including those found, assembled, Much of the development of mechanically actuated instruments or designed by the performer. We describe the principles that has centered on robotic music systems. Kapur provides a survey of influenced our interaction and mechanical design. Finally, we robotic instruments from multiple instrument families, including document performance gestures that we saw emerge in pianos, turntables, percussion, string, and wind instruments in [10]. In demonstrations on an initial implementation of the system, which the same paper, he defines the robotic instrument as “a sound-making suggest directions for future development of similar systems. device that automatically creates music with the use of mechanical parts, such as motors, solenoids and gears.” This level of autonomy, 2. ACTUATED INSTRUMENTS though a key component of robotic musical instruments, can exist Actuated instruments have recently received significant attention in with varying degrees of human input. The robotic Indian drummer NIME and related communities. Examples from multiple instrument MahaDeviBot pulls rhythmic patterns from a database derived from families utilize excitation techniques that generally fall into three pre-recorded examples and live input from human drummers [11]. It categories: electromagnetic, transducer-driven, and mechanical. also reacts to sensor and tempo tracking data from a human There is insufficient scope to comprehensively enumerate examples performing on the ESitar. Shimon, the four-armed marimba playing in each category here; rather, we discuss a few of the projects that robot with a pseudo-anthropomorphic head, automatically were influential in our work. improvises chords, rhythms, and melodies in sync with a human Electromagnetic actuation has perhaps seen the richest player [9]. development to date. Electromagnets placed near a ferromagnetic Non-robotic mechanically actuated instruments, that is, devices material, such as a steel string, are driven with amplified signals to that depend on human input to function and do not generate material induce acoustic vibration. A variety of signals may be used, from sine of their own, have probably received the least attention to date. tones to white noise to recorded samples, with differing results. The RobotHands uses human performance input on a NovInt Falcon strongest responses are achieved when the source sound contains force-feedback device to transmit real-time and recorded gestures energy at a resonant frequency of the actuated object. There are through a virtual connection [15]. An interesting aspect of currently at least two versions of pianos augmented with addressable RobotHands is that performance information can be sent electromagnetic actuators [2,12]. McPherson details strategies to simultaneously to multiple devices from a remote location. A similar improve this system using low-cost components that can cover the project, Stapleton and Davis’ Ambiguous Devices, approaches entire range of the keyboard and a signal processing method to mechanical actuation as a means to transmit the gestures or ensure that signals remain phase-locked with the motion of the “presence” of the performers across locations on a single distributed 11 Proceedings of the International Conference on New Interfaces for Musical Expression, Baton Rouge, LA, USA, May 31-June 3, 2015 musical instrument in which the input and output does not experiments were conducted with various audio source signals to necessarily have a one-to-one relationship [18]. For example, a strike excite the steel, including prerecorded audio samples and live input on a percussive instrument on one end may cause a turntable motor from a voice and guitar. As expected, and as is mentioned in [12], to spin on the other. Gurevich’s Stringtrees distributes performance results are very weak unless the excitation source signal contains between a mechanical actuator—a central rotating plectrum-arm— significant energy at a resonant frequency of the instrument. With our and human performers who can both adjust the speed of the rotation sample of untreated scrap metal, these resonances did not necessarily and manipulate the strings as they are struck by the plectrum-arm [8]. conform to concert tuning or the harmonic series, nor were they particularly narrowband, so while explorations with voice produced 3. MOTIVATION some interesting results when searching in microtonal steps and For the current project, we were primarily interested in exploring sweeps, similar to those achieved with sine tones in the original non-robotic mechanical actuation. This was born in part out of design, results from other sources were lackluster. frustration with the limitations of our first foray into actuated Appropriation of found objects and materials is a common instruments, a device called Metal Mirror. This instrument is built phenomenon in the world of percussion. In these instances, the from a large 2’X3’ sheet of scrap steel actuated by a surface-mounted unique timbres resulting from indistinct or weak resonances, a transducer and amplified with a contact microphone. The sheet of departure from the expertly tuned bars of marimbas and vibraphones, steel is suspended from a low wooden frame, putting the performer in are usually the aim of the instrument search. Indeed, a great deal of a meditative kneeling position face-to-face with the metal (see Figure standard percussion repertoire requires the performer to essentially 1). The transducer is driven with sine tones generated in a Max patch build an instrument out of found parts. For example, John Cage’s that also uses a webcam to track the positions of blocks that can be 27’10. 554” for a Percussionist asks the percussionist to build a setup magnetically attached and moved around the surface of the sheet. By from metal, wood, and skin. In the more recent Anvil Chorus by moving these blocks, the performer has control over subtle David Lang, the composer specifies only: “three resonant metals, adjustments to the tuning and amplitude of the sine tones. Since the four non-resonant metals, four foot pedal-operated non-resonant scrap material was not tuned or modified outside of a few holes metals, one foot