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So what is a Synthesizer Voice?

To get a better picture we need to take a slight detour and peek at the history of synthesizers. It is not particularly easy to identify a specific point in time or a place when synthesizers became a reality. Just as it happens with ideas, several brilliant minds in different parts of the world started tackling the prospect of creating electronic music instruments on the edge of the 19th and 20th century. From that moment, variations on the concept started spreading in all directions, resulting in some extraordinarily bizarre and fascinating instruments. However, much of the defining principles of synthesizers, as we know them today, can be traced to the work of one man—Harald Bode.

Bode grew up in Hamburg, Germany in a family where music played a very important role. After he lost his parents at the age of 18, he dedicated himself to studying mathematics, physics, and natural philosophy at the University of Hamburg. After graduation, Harald started working on electronic music instruments, and in 1937 he created the Warbo-Formant Organ—a radical new polyphonic instrument that produced entirely electronic tones. Like many modern synthesizers, it had a system of dynamically allocating four discrete tone generators to all of the 44-keys of the keyboard. Between that point and the late ‘50s, Bode developed several more ingenious electronic instruments, most of which were mono- or duo-phonic. This was due to many difficulties associated with stabilizing the tuning of the polyphonic Warbo.

Bode with his Audio System Synthesizer

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In 1960 Harald presented “A New Tool for the Exploration of Unknown Electronic Music Instrument Performances”, later known as Audio System Synthesizer, to the Audio Engineering Society—thus the modular synthesizer was born. This invention influenced many of Bode’s contemporaries, including Vladimir Ussachevsky, Robert Moog, and Don Buchla, who later implemented many of the concepts and ideas developed by Bode into their own work. Over the next few years, Harald closely collaborated with Moog, and his designs became integral in the creation of what we know as Moog Modular Synthesizer.

Although the open exploratory nature of modular synthesizers resonated with several composers and musicians who tried to break away from tradition, the majority were still looking for ways of adapting those new synthetic timbres to familiar musical forms. A specific way of interconnecting a VCO, VCF, VCA, and EG proved to be a great combo for sculpting new timbres while still generating individual notes that could be organized much like notes on any traditional musical instruments. This particular combination of modules became a definitive blend that we now know as Synth Voice.

A typical synth voice patch

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Despite the fact that synthesizers started penetrating popular culture with such recordings as Switched-On Bach by Wendy Carlos and the self-titled Emerson, Lake & Palmer album, big modular synthesizers were still inaccessible to the greater public, so the market drove manufacturers to develop more compact and cost-effective versions of the instrument leading to the creation of portable monophonic synthesizers like Moog's Model D, aka Minimoog. Minimoog was a single-voice synthesizer, although it featured three oscillators and a dedicated noise generator that could all be blended together in an onboard mixer resulting in rich, harmonically complex tones. On top of the amplitude envelope, Minimoog was also equipped with a second EG dedicated to shaping the contour of the filter cutoff frequency. This brings forward the idea that on top of the expected minimum list of modules required to makeup a synth voice, there is plenty of room for creativity and expansion.

Oberheim 4-Voice

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The next step was polyphony. Full polyphony on a synthesizer entails that every note of the keyboard is assigned to a dedicated voice. Historically, there was only one commercially available synth built around this architecture, Moog's Polymoog, and it proved to be an extremely expensive and not particularly reliable. The one-voice-per-key design wasn’t practical, but in truth, there aren’t many real-world situations when a performer would need to press all the keys on a keyboard at the same time. There had to be a solution for having fewer voices dynamically addressable from the same keyboard, much like in the early design of Warbo-Formant Organ by Bode, yet adapted to new transistor-driven manufacturing. The solution appeared in the ‘70s in the form of logic circuits that could cost-effectively handle voice-to-note allocation systems. This influenced the emergence of some of the first commercial polyphonic synthesizers, such as the Oberheim 4-voice. At this point quantifying polyphony with a number of "voices" in a synthesizer became standard. Hopefully now, phrases like “two oscillators per voice” or “one filter per voice” should make more sense to you if they seemed confusing before.

Although designing polyphonic synthesizers based on the wildest of your dreams is not super common in the Eurorack format of modular synthesizers, it is certainly possible and there are plenty of full-featured voices built around various synthesis concepts to make this a reality. But polyphony is not a requirement to enjoy the benefits of Full Voices. With all the essentials in place, they are a great way to achieve rich sonic results with minimum patching and thus serve as a great point of departure to explore the world of synthesis. In the remainder of this article, we’ll explore a few Full Voice Eurorack modules based around different synthesis paradigms.

Moog Mother-32 is a stand-alone semi-modular synthesizer that can be seamlessly integrated into a Eurorack system. The module is equipped with all of the necessary parts to deliver that rich, unmistakable Moog sound, in large part derived from the classic ladder filter. Mother-32 also features an on-board keyboard and a programmable 32-step sequencer which can also be used to control other modules in your system as it keeps growing.

Analogue Solutions (now-discontinued) Treadstone has everything an analog synth voice should have, and more than that. Besides the traditional subtractive VCO+VCF+Envelope+VCA combo, Treadstone features a dedicated sub-oscillator for extra bass, as well as a digital delay circuit. The module can be seen as a self-sufficient monophonic synthesizer, as all of its sonic capabilities are supplemented with a looping sequencer and a dedicated modulation oscillator. However, there are plenty of patch points on the module so that it can seamlessly integrate into a larger Eurorack system.

Olitronik Circuits's (now-discontinued) Micron is a compact, yet full-featured analog synth voice. Similarly to Treadstone, it is equipped with an additional sub-oscillator. The onboard filter can be driven into self-oscillation, and it features an auxiliary input for external signals. The most distinct feature of the Micron is its master overdrive circuit, which can act as a simple enhancer or as a much more extreme distortion effect.

As I’ve touched upon earlier in the article, as long as there are elements in place to create articulations that separate individual notes, there is plenty of room for improvisation on what goes into a synthesizer voice. Digital format offers a lot of avenues for experimentation, making it possible to explore new types of synthesis and drastically decrease the cost of production, as well as the size.

Mutable Instruments Plaits is an incredibly powerful voice based on 16 different synthesis models—and though it has been discontinued, it has several modern third-party alternatives, such as After Later Audio's Pixie. It is as easily capable of generating dreamy melodies as it is glitchy percussion, and even speech synthesis. Essentially an improved and streamlined version of MI’s previous module Braids, Plaits truly takes the “macro-oscillator” concept to the next level. A clever normalization allows the module to be used as a free-running oscillator, but as soon as a patch cable is inserted into the ‘Trig’ input, an internal envelope is applied, and the module can be used as a full voice. The tone is defined by the ‘Timbre’ parameter knob that shapes the color of the sound in various ways depending on the selected algorithm. SSSR Labs (now-discontinued) Kotelnikov is technically more on the ‘wavetable oscillator’ side of things, but the on-board transient generator with a dedicated output easily allows it to be used as a full synthesizer voice. With a total amount of 80 waveforms, Kotelnikov provides loads of sonic textures. The internal fixed filter provides options to either keep the raw high-end of the waveforms crisp or remove it with a flick of a switch. The envelope generator can function in one of 3 modes—triggered AR, AD, or looping. The range of the envelope can also be altered between ultra-slow, normal, and snappy fast. Oddly, the envelope is not routed internally to the VCA circuit but instead set to control wavetable morphing and frequency modulation. However, the dedicated output allows it to be physically routed into the AM input, effectively shaping the amplitude level of the built-in VCA. Oh, and since the VCA is bipolar, the AM input can also be used for gnarly ring-modulation effects.