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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Theory And Examples Of Ring Modulation

Ring Modulators have been around a long time and were very popular on the earliest of synthesizers.  Still popular today, the number of users has grown to include guitar players and others looking for a unique sound. A Ring Modulator needs 2 inputs to produce any output but on most units there is a internal oscillator that will function as one of the inputs. The internal oscillator is usually referred to as the “carrier” and many times can be voltage-controlled from an external source. The ring modulator produces sum and difference frequencies between the interaction of the carrier oscillator and the audio input signal. So if the carrier frequency is 1000 Hz (Cycles per Second) and the audio input frequency is 800 Hz, the Ring Modulator’s output will be 1800 Hz and 200Hz. Depending on the make and model of the Ring Modulator you should not hear the carrier oscillator or the input audio waveform, although in real world use, you may hear some leakage through the unit. Many models will also have a internal Low Frequency Oscillator (LFO) tied into the carrier, this LFO will modulate or change the frequency of the carrier to expand the range of Ring Modulator effects even more. The LFO is used to create slow effects like tremelo or vibrato and may have the choice of several waveforms such as sine, triangle or square wave. Also the LFO should have an “amount” or “drive” control that allows the user to select exactly how much of the LFO effect should be applied to the carrier. Typical frequency range of an LFO may be .1 Hz to 30 Hz. The carrier oscillator may range as low as 1Hz to a high of 3 to 7KHz.

Helmholtz has an entire chapter on the sum and different frequencies in his landmark work, “On The Sensations of Tone”, here is a small excerpt:

“It is the occurrence of Combinational Tones, which were first discovered in 1745 by Sorge, a German organist, and were afterwards generally known, although their pitch was often wrongly assigned, through the Italian violinist Tartini (1754), from whom they are often called Tartini’s tones.”

“These tones are heard whenever two musical tones of different pitches are sounded together, loudly and continuously. The pitch of a combinational tone is generally different from that of either of the generating tones, or of their harmonic upper partíais. In experiments, the combinational are readily distinguished from the upper partial tones, by not being heard when only one generating tone is sounded, and by appearing simultaneously with the second tone. Combinational tones are of two kinds. The first class, discovered by Sorge and Tartini, I have termed differential tones, because their pitch number is the difference of the pitch numbers of the generating tones. The second class of summational tones, having their pitch number equal to the sum of the pitch numbers of the generating tones, were discovered by myself.”

So it was Helmholtz himself that discovered the sum component of the combinational tones.

Here is a chart from his book that describes combinational tones that are generated from various inputs.

Sum And Difference Chart

Sum And Difference Chart

We can use this chart, constructed over 100 years ago to, calculate the output of a Ring Modulator if certain musical ratios are presented to the X and the Y inputs of the modulator. The first interval listed is the octave, but that ratio may not give a very interesting output. So lets try the next interval listed, the Fifth. With the Fifth’s natural frequency ratio of 2:3, the output will have a fundamental frequency that is one octave lower than the lower of the two inputs. This should not sound like the typical output of a Ring Modulator and may be more musically useful to some composers.

This is an example of a vocal sample and sine wave input.  To try to make some valid comparisons of the various sounds, I played a simple C scale for all examples.

Vocal Sample and Sine Wave Input

Vocal Sample and Saw Wave Input

Square Wave and Triangle Wave Input


Ring Modulation of Basic Waveforms with Doepfer A114 Ring Mod;

Helmholtz-Introduction To One of The Greatest Scientific Works In History

Hermann Ludwig Ferdinand von Helmholtz

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In the present work an attempt will be made to connect the boundaries of two sciences, which, although drawn towards each other by many natural affinities, have hitherto remained practically distinct—I mean the boundaries of physical and physiological acoustics on the one side, and of musical science and esthetics on the other. . The class of readers addressed will, consequently, have had very different cultivation, and will be affected by very different interests. It will therefore not be superfluous for the author at the outset distinctly to state his intention in undertaking the work, and the aim he has sought to attain. The horizons of physics, philosophy, and art have of late been too widely separated, and, as a consequence, the language, the methods, and the aims of any one of these studies present a certain amount of difficulty for the student of any other U of them ; and possibly this is the principal cause why the problem here undertaken has not been long ago more thoroughly considered and advanced towards its solution.

Hermann Helmholtz

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