The magnetic resonator piano (MRP) is a hybrid acoustic-electronic instrument augmenting the grand piano. By using electromagnets to induce the strings to vibration, the MRP allows the performer to continuously shape the sound of every note.
The design of the acoustic piano has been essentially unchanged for over a century. The instrument's ubiquity and versatility mask a surprising limitation: once a note is struck, the performer has no means to alter its sound before it is released. Consider the following simple gesture which is impossible on the piano:
Though some electronic keyboards allow the performer to shape a note after it has been sounded, few if any match the richness and expressivity of the acoustic piano. No concert pianist would choose even the most sophisticated digital piano over a moderate-quality acoustic grand. The MRP combines the rich sound of the acoustic piano with the flexibility of digital synthesis by augmenting, rather than replacing, an acoustic instrument.
The MRP preserves all the sounds and techniques of the acoustic piano, while expanding its vocabulary to include:
Crescendos (including crescendos from silence)
Harmonics on each string (8 to 16 harmonics are usable on the lower strings)
New timbres which can be shaped in real time
Subtle pitch bends
In contrast to the conventional (hammer-actuated) piano sound, the sounds of the MRP are pure and ethereal, emphasizing the fundamental frequency of each string over its high partials.
Comparison of spectra for traditional piano (left) and MRP (right). MRP example uses sinusoidal actuator waveform. Other spectra are possible by varying the signal to the actuators, though none exhibit the number of upper partials seen in the piano waveform.
The following video presents clips from a recent performance of Secrets of Antikythera by Andrew McPherson. In this video, the MRP is played both from the piano keyboard and a secondary keyboard atop the piano, each of which are configured to produce different sounds.
Electromagnetic actuators directly induce the strings to vibration, bypassing the piano's percussive hammer mechanism. The actuators work on the principle of ferromagnetism, in which a magnetic field exerts a force on the ferromagnetic (steel) piano strings.
Exploring the relationship between expressive intent and physical gesture in piano performance allows us to better understand creative musical expression at the piano keyboard and to refine the design of the MRP to allow it to respond more intuitively to beginner and expert performers.
A. McPherson. The magnetic resonator piano: electronic augmentation of an acoustic musical instrument. Journal of New Music Research 39 (3), 2010, pp. 189-202. Link
A. McPherson and Y. Kim. Augmenting the acoustic piano with electromagnetic string actuation and continuous key position sensing. In Proceedings of the 2010 International Conference on New Interfaces for Musical Expression (NIME 2010), Sydney, Australia. [PDF]
A. McPherson and Y. Kim. Toward a computationally-enhanced acoustic grand piano. In Extended Abstracts of the 28th ACM Conference on Human Factors in Computing Systems (CHI 2010), Atlanta, GA.
A. McPherson and Y. Kim. Multidimensional gesture sensing at the piano keyboard. In Proceedings of the 29th ACM Conference on Human Factors in Computing Systems (CHI 2011), Vancouver, BC. PDF available from QMUL MRP page.