- Hugh Davies
An Electronic organ developed at the Massachusetts Institute of Technology in Cambridge about 1929–30 by Arthur C. Hardy, with Sherwood F. Brown, on the basis of ideas by Du Val R. Goldthwaite of New York. All the pitches in each timbre were produced by a single rotating photoelectric tone-wheel on which the frequencies of 71 notes were photographically recorded as variable area or variable density waveforms, arranged concentrically; the waveforms were based on analyses of those produced by conventional instruments, such as a large pipe organ. The wheel rotates between a light passing through an optical slit, and a photocell, producing output currents of various timbres. In most tone-wheel instruments 12 wheels are used, one for each note in all octaves. With only one tone-wheel, those frequencies whose waveforms do not fit onto the wheel an integral number of times will produce rotational-frequency clicks due to sudden phase shifts between the beginning and end of a given circular track; to avoid this, each incomplete waveform was divided into minute sections and spread equally around the wheel between the individual cycles of the waveform concerned. (B.F. Miessner, ‘Electronic Music and Instruments’, ...