Tonewheels: A Brief History Of Optical Synthesis

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“The technology of synthesizing sound from light is a curious combination of research from the realms of mathematics, physics, electronics and communications theory which found realization in the industries of motion picture films, music, surveillance technology and finally digital communications. As such, it’s history is an interesting cross section of 20th century history, reaching from the euphoria of the late 19th Century and early 20th Century inventors (who often struggled between “scientific” and “supernatural” explainations of their work) through the paradigm-smashing experiments of the Soviet avant-garde in the 1920’s and 1930’s to the cynical clash of ideologies of the Post-war years and finally to the dawn of the digital era in the 1970’s.

On The Sensations Of Tone-Helmholtz

“In 1863 Helmholtz published Die Lehre von den Tonempfindungen als physiologische Grundlage für die Theorie der Musik (On the Sensations of Tone as a Physiological Basis for the Theory of Music), once again demonstrating his interest in the physics of perception. This book influenced musicologists into the twentieth century.”

Acoustic Levitation Chamber

Acoustic Levitation Chamber


“Acoustic levitation is a method for suspending matter in a medium by using acoustic radiation pressure from intense sound waves in the medium. Acoustic levitation is possible because of the non-linear effects of intense sound waves.

Some methods can levitate objects without creating sound heard by the human ear such as the one demonstrated at Otsuka Lab, while others produce some audible sound. There are many ways of creating this effect, from creating a wave underneath the object and reflecting it back to its source, to using an acrylic glass tank to create a large acoustic field.

Acoustic levitation is usually used for containerless processing which has become more important of late due to the small size and resistance of microchips and other such things in industry. Containerless processing may also be used for applications requiring very high purity materials or chemical reactions too rigorous to happen in a container. This method is harder to control than other methods of containerless processing such as electromagnetic levitation but has the advantage of being able to levitate nonconducting materials.

There is no known limit to what acoustic levitation can lift given enough vibratory sound, but currently the maximum amount that can be lifted by this force is a few kilograms of matter. Acoustic levitators are used mostly in industry and for researchers of anti-gravity effects such as NASA; however some are commercially available to the public.

This is an acoustic levitation chamber that was designed and built in 1987 by Dr. David Deak, as a micro-gravity experiment for NASA related subject matter. The 12 inch cubed plexiglas Helmholtz Resonant Cavity has 3 speakers attached to the cube by aluminium acoustic waveguides. By applying a continuous resonant (600 hertz) sound wave, and by adjusting the amplitude and phase relationship amongst the 3 speakers; the ability to control levitation and movement in all 3 (x,y,z) axis of the ambient space is possible. This research was used to show the effects of micro-gravity conditions that exist in the space shuttle environment in orbit, but done here on Earth in a lab.”


Helmholtz double-siren


“Hermann Ludwig Ferdinand von Helmholtz (August 31, 1821 – September 8, 1894) was a German physician and physicist who made significant contributions to several widely varied areas of modern science. In physiology and psychology, he is known for his mathematics of the eye, theories of vision, ideas on the visual perception of space, color vision research, and on the sensation of tone, perception of sound, and empiricism. In physics, he is known for his theories on the conservation of energy, work in electrodynamics, chemical thermodynamics, and on a mechanical foundation of thermodynamics. As a philosopher, he is known for his philosophy of science, ideas on the relation between the laws of perception and the laws of nature, the science of aesthetics, and ideas on the civilizing power of science. A large German association of research institutions, the Helmholtz Association, is named after him.”

No sound for the first minute, then sounds like a variety of instruments including a vocoder.

The Worlds First Synthesizer (Late 19th Century)

Worlds First Synthesizer

Worlds First Synth Closeup

Helmholtz Synth Drawing

This ingenious device, designed by Herman von Helmholtz XR (1821-1894), was the very first sound synthesizer: a tool for studying and artificially recreating musical tones and the sounds of human speech.


Suppose I sing the word ‘car’ and then on the same note sing ‘we’. The two vowel sounds will be similar in so far as they have the same pitch G , yet they have a clearly distinct sound quality, or timbre G . What is it that accounts for this difference, and the timbres G of musical sounds in general? Helmholtz set out to answer this very question in the mid nineteenth century, building on the work of the Dutch scientist Franz Donders (1818-1889).
Complex tones

Helmholtz showed that the timbre G 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 G of 440Hz G . But the sound does not only contain a simple “fundamental” vibration at 440Hz G , but also a “harmonic series” of whole number multiples of this frequency G called “overtones” (e.g., 880Hz G , 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 G .
How the synthesizer works

Helmholtz’s apparatus uses tuning forks, renowned for their very pure tone, to generate a fundamental frequency G 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.

By varying the relative intensities of the overtones, Helmholtz was able to simulate sounds of various timbres G and, in particular, recreate and understand the nature of the vowel sounds of human speech and singing. Vowel sounds are created by the resonances G of the vocal tract, with each vowel defined by two or three resonant frequencies G known as formants. When we say or sing ‘a’ (as in ‘had’), for instance, the vocal tract amplifies frequencies G close to 800Hz G , 1800Hz and 2400Hz amongst others. When we require a different vowel sound, the muscles of the throat and mouth change the shape of the vocal tract, producing a different set of resonances G .

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