A Method for Changing the Frequency of a Complex Wave
Earle L. Kent · The Journal of the Acoustical Society of America · 1942
This method makes it possible to change the fundamental frequency of a complex wave and retain essentially the same wave shape. For example, suppose it is desired to analyze the harmonic content of a wave whose fundamental frequency is, say, 25,000 c.p.s. With this frequency changer it is possible to divide all frequencies in that wave by the same number and keep the relative amplitudes and phase relations between the partials the same, This being true, a conventional wave analyzer having a range from 20 to 16,000 c.p.s. may be used to analyze a super audio-wave. It might be useful also in studying musical tones for it is possible to change the pitch of a tone without altering its wave form. The method may be performed by simple circuits using conventional radio tubes and components or it can be done with greater precision with a special, but simple, cathode-ray tube. This method is limited to applications where it is desired to reduce the frequency of a wave and the highest significant partial in the reduced wave must be lower than the fundamental frequency of the original wave.