In 1860, in the course of researching the science behind musical notes, Hermann von Helmholtz created a musical instrument that can be described as a synthesizer. Here’s more from Harvard:
Helmholtz showed that the timbre of musical notes, and vowel sounds, is a result of their complexity: just as seemingly-pure white light actually contains all the colors of the rainbow, clearly defined musical notes are composed of many different tones. If you play the A above middle C on an organ, for example, the sound you hear has a clearly defined “fundamental” pitch of 440Hz. But the sound does not only contain a simple “fundamental” vibration at 440Hz, but also a “harmonic series” of whole number multiples of this frequency called “overtones” (i.e., 880Hz, 1320Hz, 1760Hz, etc.). Helmholtz proved, using his synthesizer, that it is this combination of overtones at varying levels of intensity that give musical tones, and vowel sounds, their particular sound quality, or timbre.
Helmholtz’s apparatus uses tuning forks, renowned for their very pure tone, to generate a fundamental frequency and the first six overtones which may then be combined in varying proportions. The tuning forks are made to vibrate using electromagnets and the sound of each fork may be amplified by means of a Helmholtz resonator with adjustable shutter operated mechanically by a keyboard.
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