Not everyone agrees, but the synthesizer format wars are over, and Eurorack is the clear winner. One of the most noticeable trends at this year’s NAMM show in January was the proliferation of synth modules in Eurorack format, with small manufacturers sharing the main hall with larger, better-known companies. Other modular formats remained almost entirely on the sidelines.
As instruments from mainstream companies like Arturia, Dave Smith Instruments, Korg, and Roland sprout control-voltage minijacks, the demand for synth modules is heating up, and enthusiastic circuit designers are happy to meet that demand. Alongside modules that handle individual synthesis duties like oscillators and envelope generators, some modules combine related functions to deliver all-in-one synthesizer voices, versatile modulation sources, data monitoring capabilities, and the like. In this article, I’ll focus on some of the more recent modules that handle multiple functions, including a few that haven’t started shipping at press time.
VCO ($547, 22HP)
This module combines an unusually stable voltage-controlled analog oscillator with a VCA and a 4-pole lowpass VCF. Renowned for its unique sound and named after an African eagle, the Bateleur VCO’s most notable feature is through-zero frequency modulation (TZFM), a near-mythical synthesis technique offering a broader range of inharmonic overtones than traditional FM. In the Thru-Zero position, carrier waveforms reverse direction whenever the modulator produces a negative frequency. (Yes, negative frequencies exist, though explaining them would take more space than I have here.)
In addition to four separate jacks for standard analog waveforms, a sub-octave jack emits a square wave an octave below. A knob for setting depth of the pulse-width modulation CV input supplements another for manually setting pulse width. Additional knobs control glide and FM amounts and filter input and output levels. The filter is unusual in that you can turn resonance only off or up full, making it a self-oscillating sine-wave source. Because it tracks so well, the self-oscillating filter makes an ideal modulator for through-zero FM. The optional 8HP Bateleur Expander module ($154) adds CV inputs paired with knobs for controlling filter cutoff, resonance, and exponential FM. It also supplies a VCA input with an attenuation knob.
Disting mk3 ($179, 4HP)
With the Disting mk3, Expert Sleepers packs an incredible number of digital capabilities into a slim form factor, including some that would be impossible with analog electronics alone. Depending on the algorithm you select, it can be an oscillator with FM and waveshaping capabilities, state-variable filter, 2-stage envelope generator, sample and hold, slew-rate limiter, quantizer with selectable scales, pitch and envelope tracker, and quite a bit more. Among its additional functions, it’s also a resonator that can generate electronic drum sounds, a phaser with up to ten stages, a random CV generator, and a delay with numerous variations, including stereo ping-pong, tape-delay simulation with variable tape speed, and sync-to-clock options with a 1.7-second delay time.
The Disting has three inputs, two outputs, a rotary encoder for selecting parameters that operates as a button when needed, and a knob for selecting values that also operates as a button. All jacks are backlit and glow red or blue to indicate positive or negative voltages. Eight LEDs in the panel’s upper section indicate the selected algorithm and parameter values. If you want to implement custom functions, Expert Sleepers supports an open-source code framework that lets you hack the module’s software using development tools you can download for free.
Rainmaker ($639, 36HP)
If you want to generate timbres you can’t get any other way, the Rainmaker encompasses effects ranging from mathematically complex echoing patterns to unearthly drones and twisted reverb-like sounds. The module combines a stereo spectral rhythm delay and comb resonator with tons of control and configuration options, allowing for deep exploration of unconventional sonic territories.
The delay section lets you employ a single tap for delays as long as 20 seconds or as many as 16 taps to create rhythmic patterns. Each tap has its own resonant filter with lowpass, bandpass, and highpass responses. Because you can push filters to self-oscillate, you can harness them as sound sources for modal synthesis. Each tap also has its own level and pan parameters, instant mute button, and granular pitch shifter that lets you specify the number of grains, grain size, and transposition range. Globally pitch-shift signals as much as an octave up or down by applying a control voltage, and specify delay time using a rotary encoder, tap-tempo button, external clock sync, or 1V-per-octave CV. Apply preset groove patterns to individual taps and stack the taps for elaborate filtering and chord effects.
The comb resonator section has up to 64 time-delayed taps whose outputs are summed. Choose preset patterns for comb-tap spacing and relative amplitudes, and select from numerous filter modes for the global feedback path. Large comb sizes (longer time delays) produce dense echo and simulated reverb, and shorter delays produce flanging and Karplus-Strongtype plucked-string and woodwind-like sounds.
Omnimod ($385, 14HP)
The Omnimod is a modulation source that serves as an envelope generator, envelope follower, LFO, and step sequencer and also combines these functions to stream four independent control signals simultaneously. Create custom modulation patterns called shapes, and then store them in 64 user presets for later recall. Each shape has five breakpoints, and you can link any number of presets for longer, more complex modulation patterns. In addition to one-shot and looping modes, you can scrub control values and trigger modulation events in numerous ways. Each segment can have modifiers that cause repetitions with different values or transitions. To quickly form unique shapes in a fluid manner, use the left encoder to select breakpoints and select modifiers, and use the right encoder to select values.
The Omnimod has four channels with corresponding inputs and outputs, as well as four LEDs whose brightness indicates their output levels. Use the inputs to control Omnimod parameters with control voltages, triggers, and audio signals. The high-contrast OLED displays modulation shapes, parameter data, and other information. Scale input signals, set thresholds to trigger events, enable envelope following, and extract or specify tempo in beats per minute on the input oscillator page. The Omnimod stores all current parameter values when you power down and then reloads them when you power back up, so you can continue editing exactly where you left off.
SEM Plus ($795, 42HP)
Introduced in 1974, pioneering synth designer Tom Oberheim’s SEM (Synthesizer Expander Module) was originally intended as a supplementary voice for monosynths, either to fatten their sound or to connect to a sequencer. By the next year, a pair of SEMs was the foundation of the Oberheim Two-Voice (TVS-1), and SEMs were later integrated into the Four-Voice and Eight-Voice models. The original SEM had two audio oscillators, a resonant 2-pole multimode filter, a sine-wave LFO, and two 3-stage envelope generators.
The SEM Plus module takes the same functionality, expands on its capabilities, adds a patch panel with 32 jacks, and houses it in a Eurorack module, making it a complete synthesizer voice for your modular system. The oscillators now offer triangle waves as well as sawtooth and pulse, and you can mix any combination of the three waveforms, a noise generator, and two external signals. ADSR generators replace the previous ADS envelopes. The LFO now offers four waveforms instead of one. In addition to looping, the LFO is capable of one-shot mode, giving it the functionality of a simple envelope generator.
Mother-32 ($599, 60HP)
Although Moog’s first foray into Eurorack can operate as a tabletop synthesizer with the included power supply, it’s also designed to be part of a modular system. Many normal connections are hardwired, but the semi-modular Mother-32 is considerably more flexible if you bypass them with patch cords. For example, you can choose between two oscillator waveforms by flipping a switch or hear both simultaneously using their outputs on the 32-jack patch bay.
A single VCO spits out sawtooth and pulse waves, with variable pulse width and both linear and exponential FM inputs. The LFO and envelope modulate pitch and pulse width. The 4-pole VCF has voltage-controlled resonance and toggles between lowpass and highpass. The single 2-stage AD envelope generator has a switch to enable sustain. The LFO has triangle and square-wave outputs, and an assignable control output offers selectable functions such as MIDI velocity or aftertouch, pitch bend, and sequencer clock. The Mother-32 also has a VCA (either open or controlled by the envelope), a white noise generator, two voltage-controlled mixers, a 1-input/2-output signal multiplier, and an onboard MIDI-to-CV converter.
The versatile step sequencer provides 64 pattern locations, each with a maximum length of 32 steps. Options for each step include gate length, rest, accent, glide on and off, and ratcheting, which subdivides a step into as many as four repeated notes for a sort of stuttering effect. The front panel has a 13-button “keyboard” for entering note data, either by playing the buttons or by entering notes one step at a time. Octave up/down buttons give the keyboard an 8-octave range.
Data ($395, 16HP)
With all that’s going on inside a modular synthesizer, it helps to visualize every aspect of signal flow possible. That’s exactly what makes the Data indispensible. It’s a display module for monitoring various signal types in numerous ways. In addition to displaying waveforms, voltages, frequencies, spectra, and tempo, the Data functions as a waveform, fixed voltage, and clock-signal generator. Four input jacks are paired with four buffered thru jacks to ensure that signals passing through are unchanged. It also has two outputs for clock and gate signals and two outputs for control voltages and audio signals. You can update the Data’s firmware to add new functions and presets via the included MicroSD card.
One of the Data’s most useful roles is as a 4-channel oscilloscope, which operates exactly like a bench scope. You can select which channel to view, scale time and amplitude, and freeze the waveform display. Because you can monitor four inputs, you can view an audio input, two modulating signals, and the audio output at the same time, allowing you to immediately grasp the relationship between audio signals and modulators. The spectrum analyzer function lets you view an audio signal’s harmonic content, and when you modulate the signal, you can see exactly how spectra changes over time. Because the Data’s voltage-controllable dual waveform generator can produce basic waveforms over a wide frequency range, and because you can specify their frequency, amplitude, and phase, you can also use it as a control source (like an LFO) or an audio source (like an audio oscillator).
Lifeforms SV-1 ($699, 48HP)
Lifeforms SV-1 is a complete synthesizer voice housed in a single module. A total of 53 patch points are available, but it also has internally hardwired connections, making it semi-modular and minimizing the patch-cord spaghetti often associated with modular synthesis. This all-in-one unit furnishes most components you’d expect in a basic analog monosynth, including two VCOs, a state-variable resonant VCF, a VCA, a triangle and square-wave LFO, and a single ADSR generator. The MIDI-to-CV converter’s 3.5mm jack accepts a 5-pin DIN connection using the included adapter. The converter section has outputs for gate and 1V-per-octave control voltage signals, as well as dedicated CV outputs for MIDI CC, velocity, and LFO messages. For controlling portamento, a Glide knob introduces lag to the 1V-per-octave output.
The SV-1’s VCOs generate sine, triangle, and sawtooth, with variable-width pulse and blade (a type of sawtooth with waveshaping options) from oscillator 1 and a fixed square from oscillator 2, with a knob for FM depth. You can use the 4-channel mixer as two 2-channel mixers by defeating the mixer’s hardwired oscillator connections. The classic Pittsburgh Modular filter has lowpass, highpass, and bandpass outputs and an attenuverter. If you prefer, you can purchase the SV-1 with one of three Lifeforms Systems enclosures that accommodate a KB-1 capacitive-touch controller.
Grendel DC-2e Drone Commander 2 ($435, 28HP)
The Drone Commander 2 is a unique sound source with a personality all its own. It features two VCOs, two VCFs, a 2-stage envelope generator, and five LFOs. Although the DC-2e is an all-in-one synth voice, its architecture is unusual enough that it can produce sounds most other synths can’t. At the same time, its focus on drone sounds make it incapable of producing most sounds that other synths can without using external CV sources.
The oscillators generate sawtooth and pulse waves, and two fixed-frequency sine-wave LFOs modulate pulse width. Three additional LFOs modulate other parameters in a cascade of pulsating effects. VCF 1 is a resonant bandpass filter with overdrive, and VCF 2 is 4-pole lowpass. The envelope controls only VCF 2, and attack time is always equal to decay time—ideal for sounds that sweep in and out. All 12 knobs are push-pull switches with different functions. For example, pulling an oscillator knob up selects a sawtooth wave, and pushing it down selects a pulse wave. Set the bandpass filter’s range by pulling the Filter knob up for midrange tones and pushing down for gritty, low-end sounds.
You can purchase the DC-2e separately from the accompanying Expander module ($109, 7HP). However, because the Expander provides all 18 patch-bay jacks and the DC-2e’s only jack is a 1/4-inch audio out, you’ll need both modules unless you’re satisfied with droning tones only.
OWL Modular ($495, 20HP)
The OWL Modular is the Eurorack version of a user-programmable open-source multi-effects pedal originally designed for guitar, adding voltage control and DC-coupled ins and outs. OWL is an acronym for Open Ware Laboratory, and most of its patches are the result of crowdsourcing. The module’s internal processor lets users create programs in C++, Pure Data, or Faust programming languages. You can also use patches created by others, of course, whether they come standard on the OWL or you download them from the Web and load them from your computer via the module’s MIDI-compliant USB port. Thanks to Web Audio and Web MIDI support, you can even preview patches in Google Chrome and then load them directly into the OWL.
Although most popular as an effects processor, the OWL is designed to handle whatever DSP tasks you throw at it. Depending on what patch you load, it can be a tempo-synced delay, dual ADSR generator, arpeggiator, wavetable oscillator, distortion processor, state-variable filter, parametric EQ, octave splitter, ring modulator, pitch shifter, or assume dozens of other personalities. In addition to the USB connector, the OWL’s faceplate has four assignable knobs, four CV attenuation knobs, and eleven jacks: two audio ins, two audio outs, five control voltage ins, one gate in, and one gate out. Both the hardware and software are open source, and you can download schematics and a digital pin-out diagram directly from Rebel Technology’s website.
System-1m ($599, 84HP)
The System-1m is a complete digital synthesizer that’s functionally identical to Roland’s Aira System-1, minus the keyboard, arpeggiator, and scatter functions, with the addition of 19 illuminated 3.5mm jacks. In addition to Eurorack compatibility, it can be a desktop synth or a rackmount MIDI module, thanks to the included power supply. Like the Mother-32 and Lifeforms SV-1, the System-1m has hardwired internal connections you can bypass with patch cords. It stores and recalls 64 presets.
The architecture furnishes two audio oscillators, a suboscillator, white and pink noise, a single filter, three envelope generators, a 6-waveform LFO, and bit-crusher, delay, and reverb effects. The oscillators generate a dozen waveforms ranging from the usual analog types to the decidedly more unusual Logic Operation, Noise Saw, and Cowbell. Each oscillator has a Color knob affecting pulse width, waveform symmetry, or detuning, and Color can be a mod destination. The filter offers simultaneous highpass and resonant lowpass responses, and you can switch lowpass from 2-to 4-pole. Two ADSR envelopes modulate the filter and amplifier, and an AD envelope modulates pitch.
Plug-Out compatibility is probably the System-1m’s most remarkable feature. It hosts soft synths that emulate classic Roland hardware, running as plug-ins on your computer or within the module. Although the System-1m is 4-note polyphonic, it becomes monophonic whenever you connect patch cords or it hosts a Plug-Out soft synth. Fivepin MIDI jacks are mounted above and opposite the front panel. A USB port, also mounted above the front panel, handles MIDI and audio data up to 24-bit, 96kHz.
Control Forge ($TBD, 22HP)
E-mu Systems founder Dave Rossum’s new company specializes in designing Eurorack modules with unique capabilities. One forthcoming module is the Control Forge, a programmable source of modulation signals that functions as an envelope generator, LFO, sequencer, or any other control-voltage source that requires precisely defined stages. The Control Forge will save and recall hundreds of presets, each with a maximum length of eight segments. You can link presets so that one follows another to create sequential lists of automated events as long and complex as you want.
In addition to each segment’s length, you can define its target level as either a specific voltage or relative to the previous segment’s voltage, optionally quantized to the nearest 1/12th of a volt. Between stages, choose from 67 transition shapes and view them graphically on the module’s color LCD. You can also determine whether any stage automatically jumps to another stage when certain conditions are met, such as exceeding a value threshold, enabling looping patterns whose evolution depends on changing conditions. Define segment levels and lengths either by manually twisting an encoder or by applying a control voltage.
You can offload the Control Forge’s entire library of presets and sequences into an optional nonprogrammable module called the Satellite ($TBD, 12HP). Once settings are transferred, use as many Satellites as you need to serve as multifunction modulation sources in your Eurorack system.
Former Electronic Musician senior editor Geary Yelton has been fascinated with synthesizers since 1967, when he saw The Monkees play one on TV.