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Getting Started with Eurorack Modules

What exactly is a Modular synthesizer?

A synthesizer is a musical instrument that creates sound electronically. And in a modular synthesizer, the building blocks of a synthesizer are broken out into separate functions. 

While many of the individual building blocks were not new inventions, both Moog and Buchla arrived at the same components:

  1. Voltage Controlled Oscillators (VCOs) that provide a sound source.
  2. Voltage Controlled Amplifiers (VCAs) that allow the sound to be loud or quiet, on or off.
  3. Filters that were able to permit only specific frequencies of sound to pass through
  4. Envelopes that were able to shape the audio signal over time
  5. Noise Generators that created random frequencies of white or pink noise
  6. Mixers to combine the signals

Mysteriously, the similarities between Moog and Buchla don’t end there.

Physics major? Check.

Musician? Definitely.

Had a mentor who was an established composer, musician, and educator? (Uh. Really?) Yup.

Herb Deutsch’s friendship with Bob Moog and Morton Subotnick’s friendship with Don Buchla was instrumental to their success. Their feedback and encouragement directly shaped the development of the synthesizer. 

The modularity was simply a byproduct of rapid iteration and feedback. Adding or changing something without completely reworking it is always much more manageable.

With everything separated, the signals must move from module to module. A musician makes those connections using cables to make a “patch.”

The term comes from the telecommunication industry. Equipment that stopped working would get “patched” to a standby unit using “patch” cables to bypass the problem. But with no issues here, we’ll use our patch cables to make connections. 

Both inventors used transistors instead of finicky vacuum tubes. But Buchla and Moog’s key innovation was that the modules were all voltage controlled. 

Those voltages could be:

  • an audio signal (a sound source in the range of human hearing)
  • a control voltage signal (CV) is used to control the different parameters of a module (such as pitch and amplitude)
  • a trigger or gate signal which is a pulsed voltage used for timing (on and off, high and low, true or false)

Let’s look at each of these in a bit more detail.

Audio Signals

If we zoom far out from our little world of synthesis and put our physicist hats on, we see that everything is just a wave of energy. Sound is ripples of energy moving particles at a frequency somewhere between 20 Hz and 20 kHz (at audio rate or within the human range of hearing).

Most traditional instruments create sound through vibration. Piano, violins, and guitars all have strings that vibrate when struck, bowed, or plucked. Flutes, tubas, and saxophones all rely on air vibrating in chambers. Drum heads vibrate when struck with a drumstick. The waves of energy bounce around inside the instrument. Those sound waves cause resonance, overtones, and harmonics. These properties give the sound its distinct character and are what our brain and ears find interesting. Each instrument’s size and shape give its unique tone and timbre.

Synths don’t have air chambers or strings and rely on the movement of speakers to create sound waves. Sounds typically start with an oscillator. They produce a synthetic vibration that becomes sound when sent through a speaker. The speaker moves back and forth with the rise and fall of the oscillator’s voltage (positive to negative). If we increase the frequency of the oscillation, the faster the rise and fall happen, the quicker the speaker moves back and forth, which results in a higher perceived pitch (note).

Control Voltage (CV)

Control voltage (CV) is simply a voltage used to change a module’s parameters. While most modular synthesizers use control voltage, module designers implement it differently. For example, Bob Moog decided that the frequency on his oscillators would respond to a scale of 1 volt per musical octave. A pitch at 3 V would be two octaves above the pitch produced at 1 V. Buchla arrived at 1.2 volts per octave with 100 mV per semitone. 

That same CV signal could control the amount of resonance in a filter or the amplification in a mixer. It’s up to the module designer to decide which parameters use CV. Often a parameter has both a knob for manual control and a CV input jack that allows voltage to “turn the knob” for you.

Changing parameters over time is called modulation. Let’s slow down our audio rate oscillator from above to under 20 Hz. In that case, it becomes a Low-Frequency Oscillator (LFO), perfect for modulation. 

Let’s turn it down to 1 Hz (one cycle of the wave every second) and patch it into another oscillator’s CV input for frequency. Once a second, the LFO’s voltage will go from low to high, raising the second oscillator’s pitch and then dropping it back down. This technique can be used subtly as a vibrato or tremolo effect or to thrill your neighbors with ambulance sounds.

Control voltage can be a powerful tool. You’ll often hear synthesists talk about “modulating the modulator,” which can provide surprising and humanizing results. For a great example, search the internet for examples of the “Krell Patch.”

Triggers and Gates

Control Voltages can be simplified further to control rhythm modules or timing signals. Triggers and gates are high/on and low/off voltages that signal the start and stop of an event. Modules often treat gates and triggers interchangeably.

Gates are significant for the time held at a high voltage. For example, a key pressed on a keyboard creates a gate that signals how long the sound will play.

Triggers are just very short gates. These bursts send signals to other modules to do something, from keeping tempo with a clocked trigger to signaling a drum module to play.

If we step back from these different signals, remember that each is just a voltage. 

Modular synthesis is so open that plugging an audio signal into a control voltage input can yield exciting results. Flip that around, and you can speed up a control voltage to audio rate frequencies making new and unique sounds.

Getting Launched with Modular Synths

What Do You Want to Accomplish With It?

Whether you want to explore sound design or build the ultimate drum machine, it’s best to have a focused idea of what you seek. Here are some idea starters:

Full East Coast synth voice? 

  • VCO
  • Filter
  • Envelope – ADSR (Attack, Decay, Sustain, Release)
  • VCA

West Coast synth voice?

  • 2 VCOs or a Complex Oscillator
  • Waveshaper
  • Function Generator – AD
  • Low Pass Gate

Looking to create your own external effects for your guitar or instrument?

  • Instrument to modular interface
  • granular synthesis
  • reverb
  • delay

Ambient sound beds?

  • reverb
  • filter
  • granular synthesis
  • physical modeling
  • sequencer

Drum machine?

  • Trigger sequencer
  • multiple drum voices
  • modulation source
  • mixer

Generative, self-playing system?

  • Function Generator
  • Precision Adder
  • Sequencer
  • VCO
  • VCA
  • Filter

Why You Should Stay Away

Getting into modular is expensive. It is a small boutique market, and production limitations can lead to FOMO (Fear Of Missing Out) and GAS (Gear Acquisition Syndrome).

Your time spent researching modules should be less than the time spent using modules.

The siren of unfilled space will call out to fill your case. Resist temptation with blank panels.

Due to the modular’s blank canvas, it is also easy to get lost without approaching the instrument with intention. Experimental production is not always productive experimentation.

The Community

Go to a meetup. Attend a performance. Visit your local synth store if you have one nearby. Ask people for advice on ModWiggler. Everyone was a beginner and usually more than happy to help. Use YouTube’s tutorials and talks as a resource. Leave comments and ask questions. 

You’ll find online communities in every neck of the social media woods, from Instagram to Mastodon to Twitter to Reddit to Facebook to Discord. Hashtags are your friends: #eurorack #synthdiy #modularsynth #sdiy

​​Try It Out. Virtually.

VCV Rack is an open-source virtual eurorack studio for your computer. Use it to become familiar with actual modules and patching techniques before spending money getting physical. There are fantastic YouTube videos from Omri Cohen that will walk you through the concepts of modular synthesis using VCV Rack. 

The Basics

At the very least, you’ll need a case and a power supply. 

Cases can be as simple as a cardboard box to as fancy as a bespoke piece of furniture. The width of a case is measured in hp (horizontal pitch) and has a height in U (rack unit). A standard Eurorack module is 3U high. is a fantastic resource for planning your case. Just drag and drop modules on the screen, and it’ll calculate dimensions and power requirements. Just be sure to note the width in hp and depth in mm of the modules to find your ideal case size.  

A “starter” case will commonly be 3U (1 row) high and 62hp – 104hp (12″-21″) wide and around 60mm deep. Many modular artists find a 6U (2 rows) high and 104hp wide case is big enough to perform with but still small enough to be focused (and fly with you in as a carry-on). 

Most cases will have rails with M3 (sometimes M2.5) sized threaded strips or sliding nuts to which you can screw the modules. 

A clean, reliable power supply is even more important than the case itself. Some cases will already have a power source installed, but there are plenty of options for cases without power.

A power supply will list amperage for +12v, -12v, and frequently +5v. A good rule of thumb is that the amperage draw of your modules should be well below 75% of your supply’s rated output. can help determine the power requirements for each voltage.

With the case unplugged, you’ll connect the power in your case to each module using a ribbon cable (typically provided with a module). The red stripe denotes the -12v side of the cable and faces down. Remember to match the markings and orientation, as plugging it in backward can destroy a module or your power supply.


Now What?

Start slow and start small. Simultaneously buying many modules will be overwhelming, so purchase one at a time. 

With each new module, consider learning it as if it were a new instrument. You should read the manual, watch YouTube videos on it, and feel free to participate in community discussions.

Discover the ins and outs of each module until you reach your system’s limitations. When you start to become frustrated, that’s when you’re ready to expand.

Starting Points

You’ll want to get the most functionality crammed in as little space when you are just beginning your journey. Using to sort and filter through modules will help you pinpoint the perfect fit. 

Full synth voices (A full voice contains a VCO, Envelope, VCA, and Filter)

  • The Doepfer A-111-6 is a full analog voice with lots of CV control, sounds excellent, and is modestly priced. 
  • Finding a Plaits or Braids module from Mutable Instruments will give you a flexible digital voice with countless synthesis options. While Mutable Instruments has discontinued its modules, its owner Émilie Gillet’s generous open-source licensing, has allowed makers to continue building upon her legacy.

Jacks of all trades:

  • Make Noise Maths is a very flexible analog function generator. It can provide two sets of envelopes and perform logic functions, mix signals, act as a VCA, or even become an oscillator.
  • Expert Sleepers Disting mk4 is a digital swiss army knife that can fill almost any gap in a system. With 80+ algorithms, the module can be changed from an oscillator to a reverb to a precision adder. This one requires a bit more practice to master.
  • ALM’s Pamela’s New Workout or Pamela’s Pro Workout is an insanely flexible clock source at the heart of many rack systems. It excels at triggering drums, providing euclidean polyrhythms, and generating interesting modulation signals.


Another great path is to start with a semi-modular synth. These often have all of the components of a complete modular synthesizer. Still, many connections between modules are “pre-patched.” Plugging a cable into a jack will bypass the normalized wiring. 

Semi-modular synths often have a VCO, envelope, VCA, and filter all in one case, including a power supply. They’re typically less expensive than buying all of the modules individually. Living with a single module in a new modular case is easy because all the essentials are already included in the semi-modular.


What’s Next to Explore?

There’s an old adage that you can never have too many VCAs—some VCAs double as mixers that can combine simple signals to make complex ones. VCAs are also great at taming control voltages using offsets and attenuation. They allow you to modulate the modulators to produce unique and exciting sounds.

Filters add character and movement to otherwise identical sounds by removing or accentuating different sound frequencies. Use low pass filters with envelopes to create a low pass gate (LPG). An LPG acts similarly to a VCA but clamps down on sound frequencies instead of amplification.

Sneaky Tips

While modules tend to hold value, you can find great deals by buying used ones.

Only some things need to go in the case. Save space using external sequencers (like Korg’s SQ-1 or Arturia’s Beatstep / Keystep) and external effects (rack mounted or guitar stomp boxes).

Eurorack audio levels have a 5x-10x greater voltage range than a standard instrument output. However, many stand-alone mixers can handle the hot signals by turning down the gain.


Online Communities:

In print:

Places to buy:

Great YouTube channels:

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