Modular Synthesis Demystified

July 23, 2013
Not unlike vinyl records, modular synths have worked their way back into the mainstream with a vengeance. Once the domain of university music departments, cerebral and deep-pocketed electronic composers, and progressive rock icon Keith Emerson, hardware modulars are now used by all sorts of musicians from working keyboardists to EDM creators such as Deadmau5. If you’re modular-curious and considering starting your own system, our mission in this article is to tell you what you need to know before spending a dime. 

Square One

While modular synths have had a reputation as being for niche enthusiasts, mainstream manufacturers like Akai, Arturia, Korg, MOTU, and Propellerhead all have products that support analog control voltage in one way or another. Remarkably, the modules themselves are more affordable than ever, and the number available has grown exponentially in the last decade. Because you can spec out every element of your synth, a hardware modular offers maximum flexibility. Best of all, you can assemble a system that fits your budget and needs, whether the synth must be portable enough for touring or fully integrated into your DAW. Many modular owners started small, researched new modules worth lusting after, and added one or two every other paycheck, building up gradually to large, impressive systems.

The web of a modular’s patch cords looks both exciting and daunting to the newcomer. But if you’ve ever run a keyboard through a chain of effects pedals, you’ve already got the idea: A modular synth is a collection of devices that you connect just like stompboxes on a pedalboard. However, synth modules offer greater flexibility than stompboxes because, in addition to passing audio, they accept and/or generate control voltages (CV), which can modify sound parameters in real time with greater resolution than MIDI. 

The first step in building a system is to determine what you want it to do. Besides their adaptability for lead and bass duties, modulars can be used for sound design; for sequencing; for signal processing pre-recorded or live input by means of filtering, waveshaping, and modulation; or for some combination thereof. Although you might configure your instrument for a specific purpose, many of its modules can do double or triple duty. For example, the filters you chose for your synth can also process drum samples from your iPad or DAW. 

While a modular gives you extensive modulation and routing options compared to a preconfigured synth, one thing you lose is instant patch recall: Every cable and parameter has to be set manually. In addition, your modular will likely be less compact and portable, especially if you’re used to virtual synths. And, of course, a modular system will cost more per feature than a “slab” synth. However, the exponential increase in sound quality and timbral diversity will be worth the extra patching time and additional desk space.

Next: Don't Be Analog Retentive


Don’t Be Analog Retentive

Though many great synth modules are analog, modular synthesis doesn’t imply analog exclusivity—nor should it. As with every other aspect of technology, digital signal processing has entered the mainstream of modular synth design. While the control signals themselves—CVs, gates, and triggers—remain analog and yield unmatched resolution, much of the innovation in this field involves onboard DSP. In general, DSP-based modules can do things that would be expensive (or impossible) with analog circuitry alone.

Just like any other class of instruments, some modules sound fantastic, some sound mediocre, and others just plain suck. For the most part, the sound quality of a module is the result of its design and construction, not whether the module has analog or digital circuitry behind the panel. 

You can still be an analog purist and assemble an affordable and versatile system. But if you want elaborate control capabilities or sophisticated time-based audio processing, such as the Make Noise SoundHack Ecophon ($399) offers, it’s worth investigating the world of DSP-based modules.

No Special Keyboard Needed

The good news is that you can use any MIDI controller to play your modular system as long as you have some sort of MIDI-to-CV converter. Many modular enthusiasts resist using MIDI, instead using the gates, triggers, and CVs generated by sequencers, LFOs, envelope generators, and other modules. 

MIDI-to-CV conversion can be done with a dedicated module or by using a standalone device. Doepfer offers a variety of MIDI-to-CV modules, as well as the A-192-2 ($190) CV/gate-to-MIDI/USB interface, should you want to control your other synths from your modular. Additional manufacturers of MIDI-to-CV modules include Analogue Systems, Analogue Solutions, Kilpatrick Audio, and Pittsburgh Modular. Kenton has a line of stand-alone converters available in various sizes and price points, while Doepfer recently introduced the Dark Link ($170), a USB/MIDI-to-CV converter based on the circuit used in its Dark Energy modules.

For high-level DAW integration of your modular, you have several options. Expert Sleepers sells a variety of hardware modules and software plug-ins that offer high-resolution, bi-directional control. Similarly, MOTU Volta (reviewed Aug. ’09) is a plug-in that sends control voltage signals through the audio outputs of compatible computer audio interfaces. A highly anticipated feature of Propellerhead Reason 7 is the External MIDI Instrument, which gives you a way to control your modules from the software’s sequencers and devices. On the other hand, if you want to control things in the other direction and synchronize your DAW to your modular system, check out the Innerclock Systems Sync-Gen II ls ($660) and Sync-Gen II Pro ($750) modules, which feature DIN sync and MIDI outputs. 

A number of keyboards that have CV and gate I/O are widely available. The majority of products by Moog Music—from the Voyager and Phatty synths to the Moogerfooger pedals—have some sort of CV/gate connectivity. These can be enhanced using the VX-351 CV Output and VX-352 CV Input expanders for the Minimoog Voyager or the CP-251 Control Processor.

Other manufacturers have noticed the growing popularity of CV/gate as a means of playing notes and tweaking your sound. Examples include the Arturia MiniBrute (reviewed Nov. ’12), the Korg MS-20 Mini, and the Akai Max25 and Max49 controllers (reviewed Oct. ’12). Because these keyboards offer MIDI over USB, they can bridge your DAW and modular synth. Although it’s pricey, my favorite controller is the Analogue Systems French Connection ($3,199), which combines a 49-note keyboard and a ring-and-wire glide control in the style of the Ondes Martenot. It’s also a controller favored by Trent Reznor of Nine Inch Nails.

Doepfer makes a variety of control products for modular systems. On the traditional side is the A-100CGK ($599), a four-octave CV/gate keyboard with three CV outputs, a gate output, and MIDI I/O; the RM2 MIDI Ribbon Controller ($399), which has a pair of CV outs, a Gate output, and MIDI I/O; as well as modules such as the A-178 Theremin Control module ($110) and the A-179LCV ($90) light-control voltage source. 

If you’re interested in other types of gestural control, Synthwerks offers a number of modules featuring force-sensing resistors. A more elaborate controller is the Make Noise Pressure Points ($215), which uses capacitive touchplates to generate gate and CV signals. Also, Eowave recently introduced a pair of Eurorack modules that generate voltages when used with the company’s extensive line of sensors that measure pressure, tilt, G-force, temperature, and other factors.

Next: Module Formats


Module Formats


Fig. 1. The height of various module formats, left to right: Eurorack, Frac Rack, a pair of 4U modules (Buchla and Serge, respectively), a pair of 5U modules, and the slightly taller (9") Cyndustries/Modcan format.


The breadth of proprietary module formats has coalesced into three main form factors—5U, Eurorack, and Fractional Rack (Frac)—with a few more that are proprietary (see Figure 1 above), such as designs by Buchla and Mattson Mini Modular. While nearly every module on the market today plays well with other manufacturers, you’ll be happier if you keep the majority of your module purchases to one rack format, because each format has its own cable needs, power supply connections, and panel dimensions. Deciding on panel and connector size is one of the biggest decisions you’ll make.


For example, Moog-style modulars have large knobs, 1/4" cables for audio and CV patching, and panels that are 5U (8.75") tall and measured in 1.75" rack units for width. These take up more space than the competing formats, but you’ll appreciate the extra panel space and large controls when you’re programming a sound through a jungle of cables. Synthesis Technology/MOTM,, Modcan, and Moon Modular are the active companies in this format. If you like a large format but prefer using stackable banana plugs for patching, check out Modcan and Cyndustries. 

Although the giant systems associated with Wendy Carlos and Keith Emerson are impressive, the instrument you assemble doesn’t have to take up an entire wall. The current market leader in modular formats is the Eurorack, which has panels that are just over five inches tall and panel widths measured in HP (horizontal pitch) units of 0.2" each. This form factor boasts 90 manufacturers and nearly 800 modules—and counting. Eurorack modules use 1/8" (3.5mm) mini jacks and have smaller controls than the 5U systems, resulting in greater feature density in a smaller amount of space—an advantage or a drawback, depending on your point of view. 

At 3U tall, the Frac Rack format is roughly the same height as the Eurorack, and also uses 3.5mm jacks. The main difference between the two is in the rack size and power supply voltage: Frac Rack requires a ±15V supply, while Eurorack uses ±12V. While this format doesn’t have nearly as many manufacturers or products as Eurorack, Frac users are a small and loyal bunch, so someone will always be supporting it. The major players in this form factor are Blacet Research, Synthesis Technology/MOTM, and Metalbox. 

Next: Cases and Power Supplies


Cases and Power Supplies

 Fig. 2. The new Doepfer case with rack rails and power supply. The unfinished wood brings the cost down significantly.
Once you’ve determined your module size and cable preferences, you’ll need a case and power supply. Many modular synth enthusiasts build their own cases. My favorite example is the 5U system of ambient composer Robert Rich, where the modules are screwed directly into a wooden cabinet he designed and built himself—simple and neat.

If you purchase a case, it’s likely to be a major portion of your initial investment. Keep in mind that a quality power supply results in reliable and low-noise audio, while a robust case protects your modules for decades.

Many manufacturers sell cases, cabinets, and power supplies separately, together, or with a complement of modules. Entire systems in the larger formats are available from, Modcan, and Cyndustries. A good source for sturdy Frac Rack frames and power supplies is Blacet Research, which just introduced its Rak-2 line ($299–$669). 

The Eurorack format has a greater number of options. On the inexpensive side of the spectrum are Tiptop Audio’s μZeus ($85) flying bus board, Zeus powered bus board ($160), and Happy Ending Kit with rack ears ($149), as well as the Doepfer A-100 Minicase ($120–$140), the A-100 DIY Kit #2 ($99), and the new A-100LCB angled case (prices TBA; see Figure 2 above). At the upper end is Tiptop Audio’s Station 252 folding case ($1,250–$1,400 without power supply) and Doepfer’s line of Monster Cases ($1,999–$3,699). In between you’ll find an assortment of cases, racks, and accessories for mounting and powering your Eurorack modules from ADDAC System, Analogue Systems, Analogue Solutions, Enclave, Goike, Gorillabox, and Monorocket. Companies offering complete systems (case, power supply, and modules) include Blacet, Doepfer, Make Noise, Pittsburgh Modular, and 

Next: Modules!

Modules, Modules, Modules

Admittedly, there is an overwhelming number of modules out there, and at first glance, building a basic system may seem an insurmountable task. But if you figure out what you need (as opposed to what you want or what looks sexy) and you use online resources such as (an interactive configurator for the Eurorack format), you can sort out a satisfying starter system.

 Fig. 3. The WMD Micro Hadron Collider is a dual VCF in Eurorack format that sounds great and offers a lot of functionality in a small amount of space.
Keyboardists who want to begin with a basic subtractive synth voice will need (at the very least) an oscillator or two, a filter, a pair of envelope generators and VCAs, an LFO for modulation, and either a MIDI-to-CV module or a keyboard controller that outputs CV and gate directly. One approach is to pick a set of modules that emulates the signal flow of a known vintage synth. For example, the Minimoog held three oscillators, a noise source, a resonant 24dB-per-octave lowpass filter, glide (portamento), a pair of envelope generators, and a mixer—in fact, it was basically a hardwiring of the most frequently recurring patch type among Moog Modular users. The Oberheim SEM, on the other hand, featured two oscillators, two envelopes, and a resonant 12dB-per-octave multimode filter. Several companies make filters that emulate the sounds of both of these instruments, and indeed, the Moog and Oberheim filter characters are different enough that serious synth players tend to want both. However, an old-school vibe is not the only way to go.

Modules typically fall into one of two design categories, with a wide difference in price and performance between them: simple, single-purpose modules or more complex, multi-purpose ones. A basic oscillator will offer basic waveforms (sine, triangle, sawtooth, and square), include a CV input or two for pitch, and perhaps have inputs to control pulse width, sync, and FM. Expect to pay around $100 for such an oscillator. Multipurpose oscillators will have additional control inputs, perhaps offering linear and exponential FM, or quadrature outputs (jacks offering the waveform at intervals of 90-degree phase differences). Both of these features greatly expand your modulation capabilities, and will ultimately take up less space in your rack because they’re integrated into the oscillator panel. Here, offerings range from about $200 to over $1,000.

Similarly, control modules run the gamut from simple to complex. A basic envelope generator has variable attack, decay, sustain, and release stages, and it might include CV inputs for each stage. A more complex version will have a retrigger function (so that the module can double as an LFO), or offer an end-of-cycle pulse output. The 4ms Pingable Envelope Generator ($345), for example, is a dual EG that can multiply or divide the trigger input, while giving you extensive control over the output shapes. 

Modulars excel at subtractive synthesis, and filters provide a lot of the action in such a system. Here, Moog-like four-pole lowpass filters abound, but there are numerous other options. Again, straightforward filters that offer lowpass, highpass, and bandpass results can be relatively inexpensive and take up little space, but a feature-rich filter will rarely sound bland and will likely cost you more. For example, the WMD Micro Hadron Collider ($339) is a dual multimode filter that offers serial or parallel processing, a phase switch, an integrated voltage-controllable mixer, and, most importantly, it sounds awesome—exactly what you want (see Figure 3 above). 

While sound quality is one of the primary goals of your system, it should also be fun to use and musically satisfying. If you examine what you like best about the synths you currently play and adapt those controller and sound aspects to the modular system you design, you’ll wind up with an instrument that will not only be sonically exciting, but will constantly inspire you to create new soundscapes and compositions.

Next: Pre-Built Starter Synth Systems

Case Study: Starter Systems


Many manufacturers sell a set of basic modules along with a case and power supply. Pittsburgh Modular, for example, offers the Cell[90] Foundation Desktop ($1,699), a great Eurorack starter synth that packs a lot of punch in a compact space. It’s designed for keyboard control and subtractive synthesis, which is sometimes referred to as the “East Coast school.” It includes a MIDI-to-CV module, two oscillators, a filter, the M2 mult/mix module for splitting and combining signals; the Modulator; a four-channel mixer/attenuator; the Toolbox, which includes slew, a signal inverter, and a noise/sample-and-hold section; and an output section featuring a pair of 1/4" line-level outputs and 1/4" stereo headphone jack. The included 15 cables are just enough to patch a moderately complex sound.


While the 13 modules in this system may look ordinary at first glance, their features greatly expand the timbral palette. The MIDI module, for example, has two gate and CV outputs and three operational modes: monophonic, duophonic, and dual mono. Duophonic lets you play two notes at once, and dual mono patches two separate MIDI channels to independent CV/gate sources, letting you (for example) play a different line on each oscillator. 

The Modulator looks like a standard ring modulator, but it offers two additional modes: Floating Z, which adds the ambient system voltage in with the ring mod output, and Linear Amplitude modulation, which sums the ring mod output with the carrier signal. This last feature produces a very rich sound and is my favorite part of this system. 

The filter also includes some interesting features. Besides offering independent lowpass, bandpass, and highpass outputs, it has an “L-H” output that, with the help of the LH knob, morphs between lowpass, notch, and highpass filter types. You can also switch to Oscillator mode, forcing the filter to resonate. The resulting tone can be blended with the input signal to create some wickedly complex timbres. 

Pittsburgh Modular offers a similar-sized Cell[90] Foundation Expander system ($1,399) that adds additional mixer, splitter, dual VCA, and dual four-stage envelope modules, as well as a multi-purpose I/O module, eight-step sequencer, voltage-controlled LFO, dual-frequency-modulated oscillator, waveshaper, and a bucket-brigade analog delay. Together, these two starter systems are very powerful yet easy to wrap your head around if you’re new to modular synthesis. 

If you’re looking for something even simpler, but with patchability, Pittsburgh sells the Cell[48] System 1 ($599), a complete single-oscillator synth voice. The System 1 is semi-modular, which means you can play it (via MIDI without having to patch anything, and the footprint is smaller. The company also offers System 2 ($699) and System 3 ($799) expansion sets.

Next: State of the Art Modular System Example

Case Study: State of the Art 


At the other end of the scale is the Make Noise Shared System ($3,189). Inspired by the design philosophy of Don Buchla, it’s an excellent example of the “West Coast school” of synthesis, where real-time modulation plays a major role in not just sound design but music composition as well.

This system includes a dual analog oscillator (DPO), a voltage-controlled filter/amp combo called a lowpass gate (Optomix), a complex LFO/envelope follower (Maths), a 16-stage sequencer (René), an “entropy generator” (Wogglebug), a balanced modulator (modDemix), a touch control surface (Pressure Points), and two signal processors (Echophon and Phonogene). Describing the features of any one of these modules would require a review-length article, so I’ll try to give the flavor of the system as a whole. 

The overall vibe of the Shared System comes from the elaborate cross-modulation capabilities of the DPO and the tone shaping of the Optomix. The DPO is a dual analog oscillator with a well-designed internal routing scheme, exponential and linear FM (simultaneously if needed), hard sync, and external voltage control over waveform, waveshaping, and harmonic content. Even without patching, this oscillator sounds fantastic.

The Optomix is a dual lowpass gate (LPG) capable of recreating classic woody percussion sounds a la Morton Subotnick. The Strike input accepts a pulse to open the gate, while the setting of the Damp control shapes the decay. The use of vactrols in the circuit are responsible in part for the characteristic timbral shift and attenuated ringing of this LPG, which is one of the best sounding on the market. The two LPGs are summed to a single output at the bottom of the module, and an Aux input is provided for mixing in an additional signal.

The Maths module could also be called a “complex function generator,” because it goes well beyond the four-stage ADSR envelope (though it can do that as well). The module has four signal inputs, two of which accept triggers and offer voltage control over rise and fall time. If you’re interested in self-generating patches that take on a life of their own, this is a must-have. 

What makes the Shared System a performance instrument is the inclusion of the Pressure Points touchpad module and the René sequencer. Pressure Points has four copper plates that sense skin capacitance, and each plate has a discreet CV output based on “pressure”—more accurately, the area of finger contact—as well as a gate output. In addition, there are four columns of three CV pots, with a CV output at the end of each row. Although precise pitch control using capacitance keys is nearly impossible, they’re exceptionally expressive as controllers. 

The René is pretty deep as far as sequencers go, but it’s easy to learn and fun to use. It starts with a 4 x 4 matrix that you can scan through vertically and horizontally using CVs patched into the X- and Y-axis clock inputs. Using two quasi-random signals from the Wogglebug, you can trace through the array in non-linear ways to get some very hip melodic patterns from either of the CV outputs, one of which is quantized. The grid of knobs can be used to tune the output voltages, while the touch pads have multiple functions such as latching and unlatching notes, or selecting programmed sequencing patterns. Finally, the René module gives you an unprecedented amount of control over sequencing for the price.


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