This paper presents the magnetic resonator piano, a hybrid acoustic-electronic instrument extending the traditional grand piano. Sound is produced without loudspeakers using electromagnetic actuators to directly manipulate the piano strings, expanding its vocabulary to include infinite sustain, notes that crescendo from silence, harmonics, and a variety of timbres. A feedback-based approach senses string vibrations from a single pickup on the soundboard, using filters and phase-locked loops to generate signals which reinforce the natural motion of each string. Signal-routing hardware enables coverage of all 88 notes of the piano using a standard digital audio interface. This paper describes the hardware, software, and performing interface of the instrument and presents measurements of amplitude, frequency response, and phase-locked loop performance. Sounds generated by the actuators achieve similar amplitudes to the traditional piano, and while they cannot replicate the rapid attack produced by a piano hammer, they complement the percussive nature of the piano by enabling continuous legato control of amplitude, frequency, and timbre.
