One of the earliest musical installations known.

9 small DC motors provided with rubber wheels are attached to a steel structure horizontally positioned and firmly clamped on a grand piano. The little wheels brush lightly certain piano strings producing a series of overtones proportional to the pressure imposed at a time to the string on its various nodal points. The adjustment of the wheel to the string is made by means of a micrometric screw (vernier). During the performance motors are noiselessly displaceable along the beam to which they are attached, so that other nodal points on different strings will be engaged.

After having set the nine motors on their respective positions on the strings, the only player moves to a different area of the stage where an analogue set of two tape/recorders in series (the first in record and the second in play-back mode) is located. One of the two machines is voltage-controlled; its speed can therefore be continuously varied, so that the resulting feedback process does not only consist in an accumulation of the same frequency but of a fluctuating wave of microtonal frequencies instead, depending on the amount of speed-variation imposed.

The whole process consists in the alternation of sound-production and sound-modification phases. It would end – ideally – when all attainable positions on the strings are reached.