An Audiofrequency Harmonic Generator System

Abstract

For proposed research in musical acoustics, a simple compact generator system is needed in which the relative phase and amplitude of each harmonic may be varied independently. In order that the fundamental frequency may be shifted freely, it is necessary to secure sinusoidal wave forms from the individual generators without recourse to electric circuit filtering. The principle of operation is similar to that employed by Firestone and also by Kurtz and Larsen. However, relative amplitude is controlled by mechanically varying the condenser gaps, while the polarizing potential remains constant. Relative phase is controlled by angular displacement of the harmonic stators relative to the fundamental stator. The theory has been developed for the rotor and stator tooth forms which will give a sinusoidal rate of change of capacity between the two elements. The theory indicates that this stator form discourages the production of even ordered harmonics of the rotor tooth form. Results of harmonic analysis of the individual generators show that the production of undesired harmonics is very low. Any remaining harmonic impurity may be eliminated by means of a cancellation principle.