Modular Synthesizers – A simple explanation

Modular Synthesizers – A simple explanation

The first modular synthesizers were quite big in the 1970s, literally. The fully equipped ‘cabinets’ of that time were taller than the average person and priceless (super expensive and not for the consumer market) but they became more compact and affordable over the years. For example, the Roland System 100M, System 700, E-Mu Modular, Arp 2500, EMS Synthi 100, Synthi AKS, Synthi A as well as various Buchla modules belong to the real classics club.

Due to the ever-increasing trend in the synthesizer sector to fall back on analog technology, the Eurorack format specified by Doepfer Musikelektronik in 1996 has developed into a real long-standing modular synthesizer format for hardware and a dominant one since 2018. The Eurorack format currently offers more than 5,000 available modules and DIY kits from more than 270 manufacturers, ranging from boutique designers to established, renowned synthesizer manufacturers known for their comprehensive range of hardware. In addition to analog modules, today there are also numerous digital modules that immensely expand the application spectrum of the modular synthesizer in Eurorack format.

But what is a modular synthesizer anyway?

Simply put, a modular synthesizer is an electronic musical instrument that consists of a multitude of different components (modules) that are used and combined to create electronic sounds. The individual modules are connected via cables (patch cables), switches, sliders and patch panels. In this way, a large number of connection options and permutations are possible. It is important to know that the parameters of analog synthesizer modules can be controlled by Control Voltage (CV).

A distinction is made between modules for generating sound (VCO = Voltage Controlled Oscillator), modules for changing sound, e.g. a filter (VCF = Voltage Controlled Filter) and modules that control the sound behaviour over time using a so-called envelope curve (VCA = Voltage Controlled Amplifier or EG = Envelope Generator). The envelope used works according to the ‘ADSR‘-principle (Attack, Decay, Sustain and Release) and shapes the resulting sound with all intermediate stages during transient oscillation up to decay. With an LFO (Low Frequency Oscillator) the resulting audio signal is modulated by a control voltage, e.g. to obtain a vibrato in the simplest case.

However, there are many other modules that are dedicated to special tasks. All analog modules are operated by control voltage: If, for example, a patch cable is used to connect the CV output of a keyboard generating control voltage or a sequencer to the CV input of a tone generation module (VCO), the control voltage changes when the keys on the keyboard are pressed, so that the receiving tone generation module (VCO) changes the pitch simultaneously. The same is done by the sequencer, which controls the connected tone generator with predetermined tone intervals and rhythmic patterns. 

Patch cables

Patch cables

However, there are also control voltages that do not result in continuous parameter changes, but are used to switch certain events. These control voltages are called ‘gate’ and ‘trigger’. The gate signal influences the time duration of an event, e.g. the duration of pressing a key on the keyboard to switch a certain parameter. The trigger signal always has the same length and triggers an event once, without influencing the course of the event. The trigger signal is used, for example, to start or stop a connected sequencer, which then simply starts and runs until it is stopped again. This is also referred to as ‘triggering’.

A connection that is made with patch cables and provides the desired result is simply called a ‘patch’. A ‘patch’ can have a simple or a very complex structure, depending on which and how many modules are connected by patch cables.

And this is where the real fun begins with modular synthesizers… but also the agony of deciding what kind of music you want to use the modular synth for. Depending on the field of application and your own ideas, you will need a number of different modules, the purchase of which can significantly shrink your savings account. At this point, you should be careful and think carefully about where you want to go.
The best advice is to start small with the essentials. How you can further expand your own modular system later on is an exciting thing, and there are many possibilities.

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What do I need for what I want to do?

The following list should help to illuminate your way in the darkness of the Eurorack jungle.


The construction of a modular synthesizer always starts with its case, because the case accommodates all modules and supplies them with power. The Doepfer A-100 LC1 Low Cost Case, for example, is suitable for beginners. It has an integrated bus board with 8 module slots and a power supply:

Upgrading is always an option. For example, the Intellijel Designs 7U Stealth Case 104 HP offers 28 slots for Eurorack modules and the practical power supply: 

Output Module

Whether a small or large system is to be created, whether it is used in the studio or for live performance, each modular system must also be connected to the outside world through a speaker system. Or you want to process external signals with the Eurorack. Input and output modules are used to take care of the audio connections to your ears and/or your audience‘s ears.

One of these modules is the Vermona Modular TAI-4 module, which offers two balanced input and output channels, each equipped with 1 jack and 1 XLR connector: 


For sound production in Eurorack, the market offers an enormous selection. Most synthesizers offer subtractive sound synthesis, and even in the Eurorack it makes sense to start with a subtractive voice when the first modular system is being planned. A subtractive voice consists of oscillators that are fed through a VCA into a filter (VCF). The whole thing is then modulated by envelopes (VCA) and LFOs.

The Verbos Electronics Complex Oscillator is a true gem of its kind and is based on the classic ‘West Coast’ principle. Triangle, square and sawtooth oscillations are offered as well as modulation of the main oscillator via FM / AM from the integrated modulation oscillator. Three waveshapers for spectral changes of the main oscillator are an integral feature. In addition, the oscillator offers numerous control options via CV.


When it comes to sound shaping, a filter module in the Eurorack is indispensable. Here the market offers a large selection of modules from different manufacturers and concepts. You really need to take a closer look and understand what these modules do if you’re aiming for a specific sound. Multimode filters are super interesting in this department, such as the Waldorf VCF1, which is beyond ordinary. The number of available inputs and outputs with their different possibilities and three distortion stages, two of which have a separate output, ensure that you can warp your sound in any direction with the VCF1 alone:

Envelope curve

Envelope parameters with modulation possibilities can create very unique sounds. This is where the Mutable Instruments Stages Segment Generator comes into play. It works as an ASR or complex 6-stage envelope, but can also be used as LFO and 4-step sequencer, which serves as a modulation source.


A modular system thrives on modulation and on how the individual components thereby
communicate with each other, so modulators (LFO) are indispensable for a lively and unique sound in the Eurorack. With the Erica Synths Modulator you get, for example, a 2-channel-LFO including noise source and 8 waveforms, which can be blended into each other whichever way you want.
MATHS by Make Noise, a multi-functional module, offers a number of further possibilities,
which can be used as an envelope, LFO, oscillator and slew limiter. A true modulation monster in the Eurorack world.


If you use several sound sources in the Eurorack, you should think about a mixer module. It is also quite useful if the mixer can also mix control voltages and has modulation inputs. Other functions are always interesting and are offered depending on the module manufacturer. The Gate Mix module from the Berlin manufacturer ACL (Audiophile Circuit League) is worth mentioning here. It provides a 4-channel mixer with voltage-controlled mute function, is solidly built and offers low-noise, neutral sound characteristics.


A modular sequencer in the Eurorack is a great thing, because it opens up possibilities to create an infinite variety of melodic and rhythmic sound structures. The market offer in this area is very extensive and it is very worthwhile to take a closer look at the different variants. A classic variant is the Doepfer A-155, for example, which is a solid example of its kind. This offers 2 switch rows with 8 steps each and can be extended by the Doepfer Sequencer Controller A-154. But there are also many other versions such as the Twisted Electrons Cells Module with which you can create very complex patches and interesting sequences.


Effects should also be considered in the modular system, because they give the sounds produced the right flavour. This is how modules differ, with their stylised texture, and this opens up completely new avenues. For example, the Radikal Technologies RT1701 EFFEXX module, with two multi-effects and 8 algorithms, plus reverb processor, which conjures a lot of sound flexibility into the Eurorack with animated stereo effects. There is also a wide range of virtual effects on the market, like Softube Clouds from Mutable Instruments for instance, a granular effect that splits the input signal into up to 16 grains in real time and offers numerous processing options such as position, size, pitch, density and texture. Physical and virtual effects are abundant, the selection is very wide, so you have to see which music genre and which effect is the best starting point for you.

Have you had any experience with modular systems and perhaps already set up your own Eurorack system? Which are your favourite modules and which can you recommend? Let us know here in the comments or on the Facebook post.

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Joe has been singing since he can remember and started playing guitar when he was 10. He's been using it as a songwriting tool ever since. He is passionate about melody and harmony and admires musicians who create these in unique ways. Check out his alternative / indie projects Best of Feelings and Zef Raček.


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