Modular Synthesis Basics (How It Works and How to Dive In)

• Learn about modular synthesis and the Eurorack format.
• Get answers to frequently asked questions for beginners.
• Explore real modular synthesis for free online!

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What Exactly Is A Modular Synth?

Have you ever seen a mass of cables and blinking lights on someone’s desk or in a studio and wondered how such an amalgamation can be a musical instrument? This device is most likely a modular synthesizer, one of the most versatile and inspiring electronic instruments in existence. Modular synths are a powerful tool for music and sound design; some musicians can compose entire albums or soundtracks with just a synth and no DAW!

Modular gives you the unique ability to create the exact synth you want from different readily available parts or modules. You could make a synth with the oscillator of a Prophet-1 and the filter of a Korg MS-20 or a clone of a Roland 303 that is sequenced by hooking it up to a houseplant. Perhaps even a theremin that has 8 voice polyphony of exclusively cat sounds. Your dad’s Microkorg can’t do that now, can it?

P.S. If you want to really get your head around sound design, Syntorial is an excellent platform to learn synthesis on (read our review).

How Does Modular Synthesis Work?

One of the core ideas underpinning modular synthesis is interconnectivity. Unlike traditional synths you may be familiar with, modular instruments are made up of several different interchangeable parts known as modules. In some ways, modular synthesizers are easier to understand than their non-modular counterparts, at least at the core level.

This is because each element of the synth can be visibly and physically separated into distinct modules, all of which perform specific roles. Though there are a few “do everything” modules on the market, most of the time a module will fit into a single category.

You can think of these modules like organs in the human body, they all work together as a system to produce a sound. To continue this analogy, they are also all connected by a system of “veins” in the form of patch cables! Let’s break down the signal flow of a typical synth patch to understand what each part does:

Control Voltage (CV)

Control voltage is how modules in the system talk to each other. Because of this, parts of modular synths are often referred to as being “voltage controlled”, i.e. voltage controlled filter (VCF) or voltage controlled amplifier (VCA).

CV inputs are commonly found wherever modulation is possible. So a filter module will have a CV input for controlling the cutoff frequency.

A common way to think of CV is as “analog MIDI” that is a continuous signal rather than a series of discrete digital messages. One cool thing about modular synthesis is that there is no distinction between control voltage and sound signals when it comes to patching. This means you can patch the output of an oscillator into the CV input of a filter for some extreme frequency modulation!

Having said this, I would not recommend patching CV signals straight into the output as they do not sound interesting on their own and may even damage your speakers.

Oscillator (VCO)

The oscillator is the heart of a synth, it gives a synth its characteristic sound and timbre. Oscillators come in varying styles and complexities, but there are a few key things to know about them.

First, in the modular world, the pitch of an oscillator is controlled by a protocol known as volts per octave or V/oct. This signal is sent via control voltage which comes from various other modules and tells the oscillator precisely what frequency to oscillate at in order to produce a musical note.

Due to the level of control we have with pitch, we can easily switch between traditional western tonality to something more atonal in a flash.

One important thing to note with modular oscillators is that in most cases they are always outputting sound, and need an amplifier and envelope to control when notes turn on and off. Some oscillators will include envelopes and other ways to gate the sound but generally this is done with a separate module.

While there are certainly dedicated LFO modules, in the world of modular many VCOs allow you to set the rate low enough to be used as a modulation source. So there is less distinction between LFOs and VCOs here – they are both oscillators and the only difference is the rate.

Filter (VCF)

If you have ever worked in a DAW and done some basic mixing or editing, you’re probably already familiar with EQ and filters to some degree.

Filters remove certain frequencies in order to shape the sound, though they can also be used to boost frequencies as well. The most common types are high-pass and low-pass filters, which remove low and high frequencies from the oscillator respectively. Another common feature of filters is resonance, a feedback control that emphasizes the center or cutoff frequency of the filter.

If you’re already vaguely familiar with synthesis, you don’t need to be reminded of the importance of filters here. Without a filter module, you are greatly limiting the range of sounds your synth can make. Unless you are really confident in your other modules, I would suggest getting at least two filters if you really want your modular rig to be a serious sound design tool.

It’s also worth noting that the filters are not just for your oscillators – you can also run audio from your DAW into them! For a guide to using external synths and effects with your DAW, check out Using External Hardware With Your DAW (Step By Step Guide).

Envelope Generator (EG)

The envelope generator in a modular synth often has two important roles.

First and foremost, it controls the volume of the amplifier usually via four common parameters: attack, decay, sustain, and release. Each of these is a stage that determines how long it takes for the signal of the oscillator to reach its peak volume, secondary volume, and then drop to zero once the note is released.

ADSR envelopes are the most common type of envelope generator, though there are more complex options available if you need them.

The other common function of the envelope is to modulate the cutoff frequency of the filter. The thing about modular synths, however, is that any of these parts can be rearranged to control whatever parameters one desires. So, the envelope generator could just as easily control the oscillator’s pitch for some interesting sweeping tones.

Because we can patch the same output to multiple destinations with modular synthesis, we can use a single envelope generator to control a number of parameters at once.

Amplifier (VCA)

The amplifier in a modular setup is one of the simplest parts to grasp in theory. At its core, it controls the volume of the oscillator via a volume knob and/or control voltage.

But really amplifiers are mostly used for gating the oscillators and other generators that would otherwise be constantly heard. Without an amplifier module, there’s no easy way to start or stop a sound!

Amplifier modules are usually quite small, and often include two or more VCAs (Voltage Controlled Amplifiers). For example, the Doepfer A-132-3 DVCA module includes two identical VCAs in one slim module, and the Mutable Instruments Veils module has four.

Sequencer

Thought of as the brain of the system, the sequencer generates musical notes by providing pitch and gate signals that can be patched into oscillators, envelopes, etc. Sequencers come in many shapes and sizes, but most revolve around playing back a predetermined series of notes in order to create melodies, basslines, or chords (assuming your rig is polyphonic).

Sequencer modules are often the main way of generating pitch and gate signals, but there are other ways to do this. One popular alternative is a MIDI module that takes notes from an external keyboard or DAW and converts them into pitch and gate control voltages.

Though a MIDI module will almost always be smaller than a sequencer module, if you go this route your modular system will no longer be “self-contained” as you are relying on a keyboard or computer to sequence anything.

Output

Modular is loud, much louder than line level, so in order to have it play nicely with other audio gear like effect pedals, most modular synths have an output module that actually reduces the hot modular level.

These also often function as a master volume control for the whole modular system.

What Is Eurorack?

Eurorack is a standardized format for modular synthesis. Since its inception in the 1990s it has quickly become the most popular format boasting the largest variety of modules and accessories. German engineer Dieter Doepfer pioneered this format with the release of the A-100 system in 1996, the first commercial use of the format that would come to be known as Eurorack.

Before this, there were many different formats of modular synth like the Moog 55 and Buchla 100 series. These synths were revolutionary in their own right, but they were not designed to work together. Eurorack fixed this problem by being a new standard format that many different manufacturers could easily adopt and manufacture. Because of its popularity, Eurorack is easily the most accessible form of modular synthesizer.

Due to the popularity of the standard, the rest of this guide will focus mainly on Eurorack.

What Is A Synth Module?

As mentioned before, modules are the building blocks or organs of a modular synth, and they can do many different things. Without these various pieces, your synth will be nothing but an empty case. Later we will cover some ways to explore all different kinds of modules, but first there are a few important things to know.

A Eurorack module is a single piece of hardware designed to do a specific synthesis job. Many different manufacturers produce modules for Eurorack such as Make Noise, Mutable Instruments, and Doepfer.

That being said, all Eurorack modules are compatible, even if they are from different companies. This is thanks to the 3.5mm input and output jacks featured on the front panels of modules that allow them to be patched together via cables. Thanks to these “mini jacks”, the Eurorack format is much more compact than other modular systems.

Of course, a module also needs power and a home. This means you will need a case to house your modules. Thankfully there are a plethora of options to choose from in all different sizes. Some popular choices include Pittsburg Modular and Intelijel. The size of Eurorack modules and cases are measured in a unit called HP (1HP=1/5 Inch) so you can check you have enough room for a module before buying!

Plugging your modules into your case requires some special attention, as in rare cases it can damage your module if done incorrectly. Here is a great video guide to ensure that you do it right the first time:

Now that the module itself is demystified, let’s look at getting started.

How Do I Get Started With Modular?

Excellent question! With the world of modular synthesis being as vast as it is, there are many ways to get started, and thankfully some of them won’t break the bank right away. Before we cover some hands-on ways to get familiar with modular, here is some philosophy to consider.

The key to getting the most out of a modular case is knowing what you want to do with it. This doesn’t mean you need to plan it out meticulously ahead of time before you start buying (though you can if you want). Rather, think about what your ideal synth would do so you can look for modules that can help you reach your goal.

Some examples of directions you could go:

• Sample-based drum rig
• Multiple oscillator complex FM tone generator
  
• Generative ambient machine
• Minimal techno system

These are examples of focused systems, but with enough space, a single system could very well do multiple things. These paths are important for avoiding a common pitfall for many first time modular users: buying lots of modules at the beginning, only to find out the hard way that they aren’t right for you.

Luckily there are some great resources available for free that can help decide what direction you want to head on your modular journey. The best alternative to buying physical modules immediately to learn modular synthesis is an application called VCV Rack which is available completely free at https://vcvrack.com.

This site has many virtual clones of well-known modules in the Eurorack format, meaning you can experiment with real modules before you have to buy them. VCV Rack can be intimidating as well, so for a guided first experience Omri Cohen on YouTube. It’s a fantastic resource with hours of tutorials on everything there is to know in this software.

Another useful resource is Modular Grid. Here you can browse the thousands of modules available to you in the Eurorack format, and virtually place them in a case of your specification. This is super helpful for planning out ergonomics, or even just aesthetics.

Modular Grid even gives estimated prices and power requirements for the modules you select. Modules can range in price from one hundred dollars to a thousand dollars each at the very high end and the exact cost of your setup will vary depending on what you want; so Modular Grid is a great site to check out if you’re trying to budget out a new rack.

And finally, there is the venerable semi-modular synth: a smaller, desktop option that saves space and money but still delivers the modular experience. These synths are often people’s first gateway into the world of modular, and for good reason. With a semi-modular synth you can learn the basics of modular, and still integrate it into a larger setup if you want to expand!

Some great semi-modular options are the Moog Mother 32 (~$600), the Make Noise 0-COAST (~$500), and the Pittsburg Modular Lifeforms SV-1 (~$600). All of these options can be removed from their case and mounted in a larger Eurorack case as well.

What Are Some Good Starter Modules?

Modular is a wild and diverse world with an almost infinite number of paths to follow and sounds to make, so picking out what modules you want to start with can be a daunting task. Thankfully there are some great staples in the Eurorack world that will fit into many different kinds of systems.

Here is a short curated list of some popular and recommended modules that are great for beginners in the modular world to sink their teeth into. However you want to focus your rack, from generative techno to ambient sampling, all of these modules would fit right in.

Mutable Instruments Plaits

• Popular oscillator with many different sound modes
• 8-12hp with clones
• $180-$250

Mutable Instruments Veils

• Quad voltage controlled amplifier
• Works as a small mixer
• Recently released v2 with new features
• 10hp

Expert Sleepers Disting Mk. 4

• Digital multi-tool module
• Has over 60 different functions
• Slim 4hp package

Other great brands:

• 2hp Modular
• Tiptop Audio
• Happy Nerding
• Make Noise

Wrapping Up

The world of modular can be overwhelming if you’re just about to dip your toe in, and can still seem intimidating even if you are many modules in.

But modular synths are fun and rewarding, capable of making all sorts of interesting and unique sounds. If you take your time and do your research, you too can build a fantastically unique synthesizer that will bring you years of enjoyment and creativity.