Eurorack's Polyphonic Awakening: How Modules Went From Mono to Multi-Voice

Not only is the Eurorack-based modular synth world bigger than ever these days, over the last few years it's been busting out of its monophonic limitations with a string of new polyphonic modules that blow the lid off the possibilities for modular synthesis. With the poly gear Doepfer and others have introduced, electronic musicians can conjure a previously unthinkable amount of magic from polyphony.

From the time Dr. Moog premiered his first system in 1964 until just a few years ago, modular pretty much meant mono. And even after Doepfer's late-'90s development of the Eurorack system helped to standardize and inspire a whole new generation of modular madness, mono was the way it stayed, unless you were willing to jump through some major hoops. The cost, space, and technical difficulty of managing modular polyphony mostly made it a no-go.

"The Eurorack was usually a mono endeavor," confirms Tom Butcher, who records under the name Orqid and also runs Seattle electronic music store Patchwerks. "I guess there have been MIDI interfaces that would allow you to do polyphony in a modular and use essentially a voice routing, times however many voices. You pair up your oscillator set with your filters and amplifiers and envelopes and then, however many voices you want you just multiply that out. That was the early way to do that stuff."

But even if you were to stubbornly pursue full modular polyphony by creating an unwieldy, prohibitively expensive Frankenstein monster with a separate filter, envelope, VCA, etc. for each voice, it would still be a beast to control. "You have to calibrate all those things," says Butcher. "If you want things to sound pretty smooth and balanced it can be a pain to tune everything up, get the amplifiers right, get all the envelopes the same."

For true modular polyphony, only a fully integrated system could circumvent all those issues, which is no snap from an engineering standpoint.

But through newly created integrated systems and inventive modules that create multiple voices out of lone CV signals, there's been an explosion of multi-voiced Eurorack modules in recent years. More than ever, synthesists can use multiple musical voices in ways that are sometimes paraphonic, sometimes truly polyphonic, and others that challenge or transcend traditional polyphonic designations.

The Games Begin

Dieter Doepfer, the founder of the company that bears his name, explains just why truly integrated polyphonic systems are so hard to design: "For polyphonic modules all parameters have to be voltage-controlled. Even parameters which are only manually controlled for monophonic modules, like input level, modulation/envelope intensity, envelope parameters ADSR, and so on. This increases the technical complexity noticeably because for each of these parameters a separate VCA is required."

That's pretty much where we were until a handful of enterprising synth sultans decided to go against the grain.

Multi-Voice Modules

One of the most important steps toward a polyphonic future was the creation of multi-voice VCO modules, like Blue Lantern's Poly Phobos, Synthesis Technology's E370, Qu-Bit's Chord, 4MS's Ensemble, the ALM/Busy Circuits Sid Guts Deluxe, Instruo's Troika, Acid Rain Technology's Chainsaw, and Supercritical's Demon Core Oscillator w/ Expander.

The Poly Phobos was an early arrival on the scene, appearing in 2017. Blue Lantern founder Flavio Mireles says, "The main obstacle to achieving modular polyphonic products in the past was cost. When I was prototyping the Poly Phobos VCO, I had to lay out the entire circuit: exponential converter, VCO generator, and wave shapers, all of this times four."

The small but significant savior that made things easier was a new version of a classic integrated circuit. CoolAudio's V3340 is a clone of the classic CEM 3440 VCO chip that pumped rocket fuel into legendary analog synths like the Prophet-5, Jupiter-6, and OB-Xa. "The CoolAudio V3340 IC chip has all of these functions internally," explains Mireles, "So instead of placing, for example, 900 SMT [surface-mount technology] parts on a circuit board, you are only placing a few."

More Poly Modules

On the filter side of things, poly-friendly four-channel VCFs like Qu-Bit's Tone and Eowave's Fluctuations Magnetiques have popped up. Rossum's eight-channel Assimil8or sampler and multi-channel MIDI-to-CV interfaces like the Bastl 1983, Analogue Solutions' Polygene, Polyend's Poly, and Mutable Instruments' Yarns opened up the poly possibilities even more. Or, you can use Ableton Live's CV Tools with DC-coupled interface modules like Expert Sleepers' ES-8.

Poly Problems

For all the new avenues these modules made available, what most of them offered wasn't technically considered full polyphony. Many of the VCOs, for example, generate chords controlled by a single trigger, as opposed to individually articulated voices. Make Noise's tELHARMONIC, in one of the more creative approaches to the single-trigger situation, uses additive synthesis to power a multi-voice oscillator inspired by one of the earliest electronic instrument's Thaddeus Cahill's 1890s invention, the Telharmonium.

Make Noise founder Tony Rolando explains, "We had this idea that while chords have a tonic and they have an interval, they have a shape, so if we were to give these three parameters voltage control, we could potentially use a three-channel sequencer to create a chord sequence. It's three voices, each voice is an additive voice that uses up to 48 sine waves to create the sound."

Musicians have found plenty of ways to work with the kind of chordal polyphony offered by VCOs like the tELHARMONIC. "It's very popular for making complex drones," says Rolando, "Your harmonics, because they're all in tune with each other… they're all gonna be related harmonically. So it's really great if you want to create a drone that's highly melodic. It's also good for creating kind of stabby chord progressions. Kind of like when you think about how people play a Farfisa organ; it's very staccato, because all the notes sound simultaneously. If you've ever played a polyphonic synthesizer you know that's rare. You never hit every note at exactly the same time. Another thing that's kind of fun is if you modulate an interval while you have a chord sounding, your chord can morph, and that can be a really beautiful thing."

This Make Noise tELEHARMONIC video shows how to create chords and progressions.

As far as filters and other types of modules, a common obstacle to fully workable polyphony was the inability to control multiple channels at once. In the case of Eowave's Fluctuations Magnetiques VCF, you might be able to do so but only have two inputs to work with. And often the modules that were unhampered by any of these constrictions came with a hefty price tag due to the expensive circuitry involved.

The word "paraphonic" has arisen as an umbrella term for modular gear that accomplishes anything short of full polyphony. "I totally understand why people want to qualify something as paraphonic versus polyphonic," allows Rolando, "because the sound is pretty different. There's something to having multiple VCOs going through multiple filters going through multiple VCAs—that's what the polyphonic sound is."

Mireles says, "Paraphonic, in my opinion, coming from a business perspective, is a cost-cutting decision. The paraphonic design only requires one set of filter and VCA, while a polyphonic design uses X amount of filters and VCAs to match the VCO count. You also need X amount of envelope generators." Of course, many of the modules that are generally pigeonholed as paraphonic could be part of a true poly system if it were wired up that way, but you'd still have the aforementioned logistical issues to contend with.

Integrated Poly Systems

The 2018 NAMM show introduced the electronic music community to some tantalizing new ideas for going poly in the modular world. Malekko and Doepfer both debuted integrated systems that allowed players to push their polyphonic desires to the limit and beyond.

Malekko unveiled a batch of modules to work in conjunction with its Varigate sequencer, which allows for simultaneous CV and gate outputs. Malekko's "ecosystem" includes quad LFO, envelope, and VCA modules, as well as an additional sequencer, the Voltage Block. A VCF module might seem conspicuously absent, but the system still provides plenty of fodder for creative minds.

Doepfer Polyphonic Modules Sounds at NAMM 2018

Doepfer unveiled quad modules for VCO, VCF, ADSR envelope, and VCA, as well as a polyphonic USB/MIDI-to-CV/gate interface, all designed to work within the context of its A-100 setup. The game-changer here is that all the voices can be controlled either independently or together. So users can achieve the kind of old-school polyphony they'd get on a traditional poly synth or they can explore the outer limits of polyphonic synthesis to their hearts' content.

"The main difference to monophonic modules," explains Doepfer, "is that the same function—e.g. a filter—is four times available with the same controls for all four sub-units. The main difference to standalone polyphonic synths is the free patching option. You may use the option for an internal pre-patched standard polyphonic synth, for example the classical VCO-VCF-VCA-2xADSR structure. But when the sockets at the front panels are used this internal pre-patching is no longer valid and you may be able to establish very uncommon polyphonic structures."

Again, the development that made this possible was the reintroduction of those all-important 3340 IC chips. As the old analog-era patents Doug Curtis (who died in 2007) created for Curtis Electromusic expired, the chips were reintroduced in 2016 by OnChip, the company he'd founded in 1988. Clones were created not only by CoolAudio but also Alfa RPAR and Sound Semiconductor. As of September 2020, there's also a brand-new VCO chip, Sound Semiconductor's SS121330, which will give new opportunities for synth designers.

"It's all pretty slim, it takes up less space, it's inexpensive, that makes it a little easier," says Tom Butcher about the Doepfer modules. "They're purpose-built for polyphony, and because of that, they're able to reduce the number of controls… compared to buying eight different envelopes. You can use a single set of controls for eight channels of a VCA for example, and that really helps you out, you don't have to spend any time calibrating the amplifiers for each voice. I think there are a small set of people for whom that's exactly what they want, and there's probably not that much else out there besides those Doepfer modules that will satisfy that."

Poly Possibilities

It's tempting (and easy) to just use modular poly gear to replicate the things you'd do with a standard polyphonic synth. But there's a far wider world of sounds awaiting those who abandon conventional configurations and think outside the box (literally). For Doepfer, that's exactly why he made his modules.

As with modular synthesis itself, the only limits are those of your own imagination. Offering up a mere few options, Doepfer says, "You can, for example, control the CVs for the VCO from a keyboard but the triggers for the envelope generators are generated by a trigger sequencer. Or you may use random sources to control the VCO pitch as well as the gates/trigger. Or you may mix the outputs not to a common signal but to four channels of a quadraphonic system. There are tons of possibilities not possible with monophonic modules or polyphonic stand-alone synths."

Viewed from a player's perspective, the colors in Eurorack's poly paint box seem even more numerous. Discussing some of his own polyphonic preferences, Butcher says, "You can use, say, three different filter types for a triad, and based on how you play and how it cycles through, you might have a different frequency cutoff, maybe one note has resonance, one has a different slope, that can introduce some sequence-like variations in the arpeggio as you play. You can be choosing from several different filters all in one ensemble voice."

A synth jam by Dieter Doepfer himself, using his Polyphonic Interface, Quad VCO, Quad Poly VC ADSR, and other modules.

Playing chords through a polyphonic MIDI interface can introduce even more fascinating twists to the process. "That's one of the things that you get out of Eurorack polyphony that you won't get out of almost all true poly synths," says Butcher. "I could have one oscillator that's analog, another voice that's like a wavetable module, another maybe a sampler, so that can get pretty fun."

Even the most basic building blocks of music itself are up for grabs if you're feeling adventurous enough.

"Once the oscillators tune out from each other," explains Butcher, "playing polyphony with the keyboard gives you these blue notes. Sometimes you'll get these microtonal shifts because it's not locked in a chromatic scale. That, for me, introduces a lot of interesting emotions, you can get an eerie or ethereal sound, and usually you can't tell when you're playing which notes will come out blue, just because you're not thinking of how the voices are allocated from the chord into the individual routing."

Make Mine Mono

Despite the promise of a bright multi-voice future hovering within easy reach, some Eurorack users remain leery of leaping into the poly pool, opting instead to stick with their tried-and-true mono modules. Even Robert Fantinatto, who documented the modular renaissance in his 2014 film I Dream of Wires and did as much as anyone to spread the word about the Eurorack universe, resides in this camp.

"I tend to agree with Bob Moog and his reluctance to do too much in the way of polyphonic synthesizers," avers Fantinatto. "Frequency modulation and other effects tend to get very muddy when you have multiple notes, and the true power of a synthesized sound I feel is best expressed monophonically. I'd be more inclined to recommend a keyboard-based solution rather than modular for polyphonic sounds, as you'd likely not be needing so much modulation flexibility when creating typical harmonies. But of course it all depends on your application."

Even manufacturers of poly products can sometimes be circumspect on the subject. Flavio Mireles says, "My general feel about the polyphonic modular market is that it is not in high demand. I am referring to individual poly products like four-voice ADSR, four-voice VCF. You need so many patch cables just to pass the signals over the next module. I believe polyphonic completed products, which contain everything but can be installed on the Euro rack would become more popular."

Doepfer himself, having created exactly the kind of system Mireles is talking about, knows better than anybody about the obstacles to true polyphony that existed until recently. "I think the main shortcomings were the many patch cables that were required for the first production series of the polyphonic modules," he says, "as these did not yet feature the internal pre-patching possibilities. I did a polyphonic modular synth many years ago. It was available only as a kit and suffered from the lack of the integrated circuits which are available today."

Now that the technology is in place, one of the main challenges for makers of polyphonic modules seems to be spreading the word to a wider audience, since Eurorack users have become so accustomed to occupying a mono world. And for some, poly gear is still seen as an extravagance. "Most people that we find coming into our shop," says Tom Butcher, "they just want to experiment with sound and they don't get into polyphony until later."

A Multi-Voice Future

With tons of room for growth, the poly modular market is bound to keep getting bigger. More products are certain to come and some are already in the works. "I'm actually prototyping another polyphonic VCO at the moment," reports Mireles, "with more wave shapes… I don't expect it to be hot seller, I just want to see how it goes." And 2020 has already brought a surge of new gear, from Qu-Bit's eight-voice physical modeling module Surface to Cherry Audio's Voltage Modular 2 system and Tubbutec's µTune quantizer/midi-to-CV interface.

Tom Butcher feels that interest in polyphony in the Eurorack universe is a flame just waiting to be fanned.

"I think there's a hunger and a desire to figure that out," he says. "It might need more education in the market to say, 'This is how you do it,' to show people how to get from where they are to the first few steps. Using something like the Rossum Assimil8or sampler, it's got eight channels and one output, so you can get polyphony on that or you can treat it as your drum kit and your bass line. That's kind of a good stepping stone to polyphony. Maybe that's what leads into the Doepfer polyphonic stuff."

The need for more education on the nuts and bolts of polyphony is an opportunity in waiting. But the man who's at the bleeding edge of the movement is the most reluctant to make predictions. "About 10 years ago I already supposed that the peak of the Eurorack boom is probably reached," confesses Doepfer. "I was totally wrong." But don't let Doepfer's humility distract from the facts—now that the poly modular genie is out of the bottle, it won't be going in again.

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