Andy Cavatorta

The Irvine is a unique crystal electrophone from a reimagined history — part of an unborn family tree of electronic musical instruments for the symphony orchestra.

These imaginary instruments have symphonic sensibilities. They are built around the sensitive shaping of individual notes. Performers can have a recognizable hand as with a cello. These instruments are designed for relationships lasting decades. The depth of techniques to discover and refine may be boundless.

Most importantly, there are no automatic features. The music comes from inside the performer and not from the instrument.

The alternative evolution ignores the conceptual vocabulary developed later for synthesizers: VCO, VCA, VCF, LFO, and ADSR envelope. Its concepts are based on Hermann von Helmholtz’s 1863 work On The Sensations of Tone [as a physiological basis for the theory of music].

Every new major technology seems to have musical applications. The early 20th Century was a boom time for novel uses for electricity. The hundreds of new instruments developed in this period range from the gimmicky to the sublime.

Many of these inventions offered new combinations of musical expressions. Adding legato to the piano. Adding glissando to keyboards. A periodic table of timbres. Microtonality. Performing by drawing, painting, or dancing.

Most of these instruments are lost or forgotten now. A new instrument finds a home in the world only when it is included in a corpus of work that people want to hear performed.

Notable exceptions include the Theremin, the Hammond Organ, the Ondioline, and the Ondes- Martenot which Olivier Messiaen used to great effect in several works.

The symphony orchestra today largely plays a role of historical preservation, performing the music of composers and cultures long departed.

But from the late 18th century to the early 20th, symphony orchestras were crucibles of musical innovation, ever expanding with new tones, timbres, textures and ideas. They were a form of nowness. It was reasonable for instrument inventors to believe that their new ideas might find purchase in this ever-expanding menagerie.

But the unprecedented horrors of World War One left Europe and North America deeply traumatized. Many ideas from before the war seemed naïve and unrelatable.

Some orchestras were open to playing the new, jarring, and unsentimental forms emerging then. But audiences were lured away from the new and old orchestral music by the nowness of jazz, blues, speakeasies, radio, and phonograph. Symphony orchestras stopped absorbing new instruments just before a golden age of electronic instrument invention.

Six gallium phosphate crystal resonators make up the source of the Irvine’s continuous analog signal path. All music produced by the Irvine is created by mixing and filtering these six signals with other software-controlled analog signals.

Many crystal resonators are designed for stability. But these are designed for use as sensors. Oscillator circuits based on these resonators produce informative patterns of distortion and instability. So the music produced contains the subtle and unique textures of the crystals.

These crystals are designed to resonate at a frequency of 6,000,000 Hz ± 150,000 Hz. This range is not musically useful; the human hearing range is about 20 Hz - 20,000 Hz. So I combine pairs of crystals that have a frequency difference of 250,000 Hz to 350,000 Hz to create our first crystal signal.

Gallium phosphate works as well as quartz in a classic quartz crystal oscillator circuit.

All physical oscillators create stable rhythms by transforming energy between two states. For instance, clock pendulums convert kinetic energy (motion) into gravitational potential energy and back to motion again.

In piezoelectric oscillators, electrical energy in the form of an electric field is applied to a crystal. This energy causes the crystal to flex and change shape, storing some of this energy as mechanical energy.

When the electric field is removed, the mechanical energy is converted back to an electric charge. If placed in a circuit that temporarily stores and reapplies this electrical energy to the circuit, the crystal-circuit system will oscillate in a stable rhythm.

Heterodyning is a signal processing technique in which two or more signals are combined and filtered to produce a lower-frequency resultant frequency. This technique was first demonstrated in 1901 and is the foundation of all radio technology.

In Fig. 1, two signals representing our crystal oscillator signals have frequencies of 6,150,000 Hz and 5,850,000 Hz. When multiplied, the resulting signal has fine rhythm around 6,000,000 Hz and a coarse rhythm at a frequency of 300,000 Hz, the difference between the two source signals.

If the fine rhythm is filtered out of the resulting signal, we are left with a 300,000 Hz signal. We use it to create signals for the second part of our signal path.

Musical timbre eludes simple definition. If we remove the pitch and loudness of a musical sound, all of the remaining character is called timbre. This is the flavor of a sound. It makes a piano and trumpet sound different when playing the same pitch.

In the mid 19th century, Georg Ohm and Hermann von Helmholtz discovered that much of timbre comes from overtones, which are higher frequency sounds combined with a fundamental pitch or sound. These are called overtones or partials. They are called harmonics when their frequency relationships fall in or close to the harmonic series.

Just as we can analyze timbres by parsing sounds into separate frequencies, we can create timbres by adding sounds together. This process was named additive synthesis by Hermann von Helmholtz, who built electromechanical synthesizers to test his hypotheses about timbres and vowel sounds.

Fig. 2 below shows how the Irvine produces an A2 pitch and its first two harmonics. These have the frequencies 110, 220, and 330 Hz.

We start with four signals with frequencies above the human hearing range that differ by 110, 220, and 330 Hz.

When these signals are multiplied together, they produce a fine pattern near 100,000 Hz and a coarse pattern of beats with frequencies of 110, 220, and 330 Hz.

When the fine pattern is subtracted by a low-pass filter, the beats become simple frequencies.

This leaves only a mix of A2 (110 Hz), and A3 (220 Hz). To the human ear, these will sound like an A2 pitch with sweet, harmonic timbre (Fig. 3).

Some sounds, like human voices, are comprised of a complex and continuous range of frequencies. Formants are broad peaks of loudness in this range. The vowel sounds we make with our voices correspond to patterns of loudness at specific frequencies. These patterns are called vowel formants.

Fig. 4 to the right illustrates the patterns of formants that create three vowel sounds. And the figures on the far right show how we shape our vocal tracts to create these formants. Vowels have properties of frontness and openness based on where we create resonances in our vocal tracts. The Irvine creates vowel sounds in two stages.

First, the voice and its overtones are sent through a subtle tube distortion to fill them out into a more complex and continuous range of frequencies (Fig. 4). Then this complex fabric of sounds is sent through four digitally-controlled universal filters that amplify or attenuate different segments of this range.

The Irvine was evolved through a discovery-oriented process that favors constant prototyping over planning and speculation. I quickly prototype forms, sounds, motions, and palettes of colors and materials with the cheapest and fastest materials. Quantity over quality. All early prototypes should look like they were assembled at gunpoint.

These prototypes are like soundings in uncharted waters. They reveal a landscape of possibilities and pitfalls. Good prototypes answer questions I had not yet thought to ask. This practice of prolific prototyping can guide one where experience cannot.

The Irvine's voice originates in gallium phosphate crystals. These crystals do not occur naturally on Earth. The techniques for growing them were developed at AVL in Graz for use as industrial sensors.

The crystals are now grown exclusively by an Austrian company called Piezocryst. They are sold in the form of flat resonator disks.

Our first challenge was figuring out how to use these ~6M Hz to create signals in the audible range from 20 Hz to ~16k Hz. We experimented with many ways to electrically alter/tune the frequency by changing aspects of the oscillator circuit.

Our second challenge was learning to stabilize the frequencies of the oscillators. We gathered extensive data while subjecting the oscillators to different temperatures, pressures, and vibrations.

A discovery-oriented prototype is usually a question, not a product. We started with questions about finger spacing and capacitive sensing circuits.

The first prototype was made with copper foil and spare parts we had on hand.

The prototyping process can move very quickly. This may be the only photo we have of the second prototype.

We see the detents cut between the keys to help a player sense distance and position.

And we see the tiny contact surface that will grow and grow with each successive keyboard design.

This pitch slider uses a ring and a loop of lanyard. It's based on the "ribbon" control of the Ondes Martenot.

The first playable prototype was built so that the musicians of NovoSonic in Munich could begin to learn the playing interface.

The third keyboard featured keys made of larger strips of copper and brass arranged like the black and white keys of a piano. This was a big improvement.

Prototype three also features three voice keys, sliders for adjusting the timbres of the three voices, and pitch transport with a ring in the style of the Ondes Martenot.

The Irvine sound circuitry was not yet finished. So Prototype 3 was sent with software to digitally simulate the crystal voices.

This prototype was a hash of many departures from Prototype 3.

The closed wooden box was replaced by parallel layers of glass circuit boards. These were beautiful. But they left the electronics vulnerable and were nearly impossible to repair.

We tested a new pitch slider that used a rail mounted under the keyboard. This was more stable and precise than the ribbon slider. And it freed the right hand to leave the keyboard.

Several new circuit designs sought to reduce the buzzing crosstalk by separating signal, data, and power lines and using one common ground line for our five types of power. These somehow made the crosstalk worse. We had a lot to learn.

But Prototype 5 was the first Irvine featuring its crystal voices, tube distortion/harmonic expander, and vowel formant controls. And I was hoping that with a little more fit and finish, this could be the final version.

The six bell jars protect the crystals from wind and vibrations in air. The six silver vacuum tubes are part of the tube distortion that gently expands the harmonics for the vowel formant phase.

Keyboard 5 featured larger keys made of brass and copper, arranged like the black and white keys of a piano. This pattern was echoed by dots and dashes above the keys.

The pitch transport has evolved into a sliding handle that leaves both hands free to move around the various controls.

The harmonics and formants were adjusted using recycled drawbars from an electric organ. Their numbered detents were the design solution for making reproducible settings.

The three voice keys feature greater sensitivity and a greater range of motion.

This is the first prototype with the full set of features! The brass knobs on the right control vowel formants and mixer functions. One knob controls the duration of a simulated three-channel tape loop.

The six pedals control the play and record functions for each of the three channels of the tape loop.

Loops can start and end anywhere within the cycle. And a crossfade smoothes the beginnings and ends together.

A tap of a record pedal starts a loop recording that ends when the loop duration has finished. A hold of a record pedal records continuously until the pedal is released. The duration before the pedal release remains recorded as a loop. A tap of a play pedal plays the entire loop on that channel until tapped again to stop. A hold of the play pedal plays until the pedal is released.

Prototype 6 reuses Keyboard 5. Though we eventually concluded that it is still challenging to visually navigate.

When keys are closer, a larger pitch range can fit under one hand. And traversing the keyboard is faster. When keys are farther apart, it can be easier to play accurately.

The space between the metal keys was intended as a compromise maintaining accuracy while providing reach and speed.

All that we have learned so far comes together in one prototype.

The keyboard has been redesigned with wide keys made of copper and brass, echoing the black and white keys of a piano keyboard. To make it easier to navigate at a glance, the pitch names were stamped into the brass keys.

This prototype also features the final concept for the instrument’s surface.

The inspiration for the form comes from traditional Austrian porcelain ceramics and their ornate flourishes.

The design was roughed out using modeling clay. This rough shape was sliced and measured. The form was reproduced and refined in a CAD program. Holes were added to the model to accommodate all of the interface elements and their mounting shapes.

The pitch transport has a robust new mechanism with internal tensioners.

The voice keys are made from slabs of aluminum with a sensitive new mechanism.

And a ‘hold’ button has been added under the performer’s thumb. When pushed, the voice levels are locked just as they are. This frees the performer to use their left hand briefly to adjust the voices, mixer, or outboard gear without stopping the sound.

The current Irvine prototype is number 8. It features the sumptuous, solid aluminum playing surface.

Irvine prototypes 5, 6, 7, and 8 are Gordian knots of intertwined and interconnected electrical systems.

There are five types of power, an Ethernet network, many stages of analog signals, and SPI, I2C, and RS-232 data lines.

All of these systems’ wires and connectors bristle with invisible electromagnetic fields that cannot be entirely isolated from one another, creating a cloud of crosstalk. Previous versions were haunted by noisy electromagnetic ghosts.

Prototype 8 features fully refactored wiring that quiets these ghosts and solves problems with different values of electrical ground.