in the early 2010s, a college kid with a MIDI keyboard and a copy of Fruity Loops. I’m still chasing that high of pressing plastic keys and hearing a thick square wave bass á la Justice or Boys Noize, made by me.

I was hooked and scrounged money together to get my hands on the Mopho. I set it up, plugged it in, and started playing. It sounded great, but I thought I had a defective module: I could only play one note at a time. This was my introduction to the concepts of monophony and polyphony, and it baffled me. I couldn’t understand how this cool-looking synth from a famous company couldn’t do what my FL soft synths could do, but little did I know that packing multiple voices into a single module was a feat that the synth community had been thinking about for decades.

Before going further, it’s useful to define what we mean when we say “polyphony”. Polyphony usually refers to the number of notes a synthesizer can produce simultaneously, but it can also refer to the number of “voices” (usually sound source/filter/amp/envelope). We’ll discuss the permutations of the term as we encounter them, and you can also check out our article on the history of polyphonic synthesizers for a detailed dive.

As I was saying, today we have a killer spread of polyphonic options, particularly in the world of modular. It took awhile to get here though: multi-voiced, feature-rich units came about through years of iteration. In a way, today’s polyphonic Eurorack modules are oddly reminiscent of the days of the rackmount synth. Prior to digital, multi-voiced instruments had to operate within the constraints of analog components (the Oberheim SEM Synthesizer Expansion Modules were a notable advancement in design), but the medium found its stride with beefier technology.

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Inspired by the SEM, Minimoog, and other devices, engineers realized that they could distill an additional voice down to its essential components and package it with the connectivity needed to slot in as a streamlined voice in an existing system. In the late 1970s, polyphonic synthesizers began to emerge and gain traction; and of course, 1983's Yamaha DX7 was both a breakthrough in polyphony and digital synthesis. Soon, the newly-ubiquitous MIDI protocol would pave the way for rackmount synthesizers such as the Roland D50 and Kurzweil K2000. The advent of a more user-friendly interface that pared back everything except for generating sound and selecting patches, as found in the Oberheim Matrix-100, is the final design milestone we need for our comparison.

As we’ll see, by interpreting the design principles mentioned above and incorporating them into their own products, today’s modular companies have created stunningly expansive modules that can easily become heliocentric in any system. Thank your lucky stars that a bunch of geniuses spent countless hours scheming and soldering so that the rest of us can sit in front of a pleasant LED glow, creating sounds that delight and amaze.

Polyphonic Eurorack Modules

Let's take a look at some popular polyphonic Eurorack modules for a sense of how this type of workflow can manifest in modern modular synthesizers.

OXI Instruments Coral

Our first entry is a powerhouse that wrangles 10 separate synth engines with an eight-voice architecture and plenty of shiny bells and whistles to boot. Within the space of 14hp, the OXI Coral manages to include Virtual Analog, Waveshaping, FM, Wavetable, MDO (multiple detuned oscillators), String, Hi Hat, Snare, Bass Drum, WAV Player, Additive, Acid, and 3VCO engines, each with their own customizable parameters.

RYK Modular Vector Wave

16 oscillators sounds like a pretty good place to start for polyphony, right? Naturally, the retro-futurists over at RYK Modular took their own unique spin by combining vector and FM synthesis under one hood and souping up the whole affair with a smorgasbord of modulation options. Lastly, it wouldn’t be a true RYK affair unless a joystick was on the table, and the Vector Wave squeezes in a cute-yet-functional one for navigating the deep waters of this module’s possibilities.

Knobula Poly Cinematic + Pianophonic

I wouldn’t be writing this article were it not for Knobula. There were modules that managed a sort of pseudo-polyphony prior to its release, but the Knobula Poly Cinematic Oscillator immediately made waves (lots of them) on its release in 2021. I remember watching Instagram videos of an empty rack save for the Poly Cinematic paired with a KeyStep and being blown away by CS80 impressions that seemed impossible for a single module, but there it was.

Starting off with a whopping 56 oscillators controlled by eight available voices, the Poly Cinematic stacks on a built-in envelope generator, multimode filter, and onboard reverb. The module is divided into sections for the EG, Filter, and Oscillators with a slew of jacks at the bottom. The three oscillator waveforms (supersaw, square, and tonewheel, which is a series of sines) can be widened with the Detune knob and further modified via the Mode switch. Again, a MIDI jack swoops in to handle your wildest polyphonic dreams (if those dreams are up to eight voices), but Knobula also included a unique Chord function which kind of acts as a bridge between monophonic triggering and polyphonic operation.

The second entry from Knobula, the Pianophonic, combines the powerful capabilities of the Poly Cinematic with the experimentalist architecture of sample and wavetable synths from the ‘90s. Also sporting eight voices, the Pianophonic’s voices each feature three wavetable oscillators and a sample engine, fertile ground for the rich harmonics and transients found in physical instruments like, well, a piano. To this end, the PIanophonic comes with an SD card filled with 16 banks of presets from hammer samples to pro-grade wavetables, and that’s only half the fun.

Staying true to its weird ‘90s forebears, the Pianophonic allows you compress, stretch, warp, and outright destroy a sound with the suite of onboard controls. The Part selector knob with all the numbers lets you rifle through the module’s available hammer samples and wavetables, either selecting a group or single samples/wavetables to pair with others according to the position of the below switch.

Don’t worry if this sounds involved and a bit labyrinthine: it is, but that’s part and parcel with the joy of diving into these polyphonic modules. At the core of the Pianophonic is the thrilling experience of hearing polyphonic keys at your fingertips that can easily morph into lush pads, deep drones, pulsating rhythms, and more.

Oh yeah, and it also has a MIDI jack.

Neuzeit Instruments Warp

Jomox Mod FM

The biggest entry in this article (by size at least), the Jomox Mod FM is a complete synth in a modular package. Measuring 56hp, it will account for a lot of rack space, but every bit of that space is devoted to eye-raising technical depth and functionality. It also has one of the most fun approaches to FM synthesis in hardware form I’ve seen in awhile.

Other Notable Entries

Over the past few years, the popularity and availability of polyphony of modules has exploded and resulted in a buyer’s market of options. For instance, the Squarp Rample is technically a four-voice sampler, but a hidden Chord mode can unlock polyphonic capabilities. The same is in play with the 1010 Music Bitbox, allowing the user to polyphonically play back sample slices. Or if you’d rather throw in the whole sonic kitchen sink, the formidable Zoia Euroburo is absolutely worth your time and money and is another module that can immediately become the anchor in your rack.

Pseudo-Polyphonic Eurorack Modules

Let's take a look at even more approaches—each offering a unique take on polyphony.

XAOC Devices Odessa + HEL Expander

There are also plenty of options to consider that find workarounds for achieving polyphony that aren’t as apparent as the previously-mentioned modules. The XAOC Devices Odessa, for example, is a formidable oscillator that employs additive synthesis and five voices for huge sounds. Similar to the Neuzeit Warp in its sound generation using 512 sine waves, the Odessa is doubly similar in that it also has an expander, the HEL, that provides 1V/oct control for each voice. If you’re looking for a polyphonic additive synthesis experience but want to forego screens, the Odessa and HEL should be at the top of your list.

Intellijel Designs Plonk

For those who can’t get enough of physical modeling and can make do with a little duophony, the Intellijel Plonk fits the bill nicely. Made in conjunction with the amazing Applied Acoustics Systems, the Plonk generates realistic, morphing exciter and resonator models of mallets, bells, drums, strings, and more. In the modeling process, the Plonk dynamically generates notes and allows them to decay without cutting off when a new note presents itself, resulting in the aforementioned duophony. While not polyphonic in the fashion that we have discussed throughout this article, the Plonk is nevertheless a fantastic module and a fantastic representation of physical modeling in your rig.

Mutable Instruments Rings

While we’re on the subject of physical modeling, why not dig into the most popular physical modeling module of all time? The Mutable Instruments Rings introduced the concept to many of us through its strummed, struck, and hammered possibilities. The Rings also delivers pseudo-polyphony in up to four “voices” through its unique operating modes cyclable via one of the buttons at the top.

The polyphony here is largely similar to that found in the Plonk: Rings is capable of allowing notes to hold and decay, so the user can hit it with a short burst of gates to create a “chord” that dissolves in surprisingly realistic fashion.

Wrapping Up

As Eurorack fans, we have an embarrassment of polyphonic riches at our fingertips in 2024. Whether you’re after a completely new experience that pairs the flexibility of modular with inventive polyphony or just want to plug in a MIDI jack and start jamming like you’re auditioning for Air, the keys are there for you. Just press a few at the same time and see what happens.

(Ed: And of course, remember—while in this article we focused on describing modules which act as self-contained polyphonic synthesizers, there are many other approaches to modular polyphony out there. Scope out our articles Tiptop Audio's ART of Modular Polyphony, Polyphonic Modular Synth: Classic Approaches, and Polyphonic Modular Synth: Modern Approaches for even more ideas about how to approach polyphony in your Eurorack system. Happy patching!)