Computer Music|June 2021
Modular, aka Eurorack, synthesis has taken the production world by storm. Here’s your complete guide on how to get going, as we go from zero to modular hero…

Eurorack has taken the music production world by storm over recent years. The hardware modular synth format essentially lets you create your own custom synthesiser by assembling modules that control various aspects of the synth signal flow yourself. The idea is that you might well end up with a collection of sounds that no other musician on the planet has. But how can you safely explore this phenomenon from the comfort of your own computer? Well, you’ve come to the right place, as this feature is designed to cover everything Eurorack!


Eurorack is a truly creative beast, and it’s one that has many heads and viewpoints. Many of these are specific to the sort of music you may wish to make, but we have to address the modularelephantine-beast in the room and discuss why anyone might want to go down the path of modular, when there are perfectly good software modulars available? The answer to this is often down to your experiences to date with synthesisers. Like any hardware music-making device, it’s the tactile approach that can feel more rewarding, and unlike off-the-shelf hardware synths, Eurorack grows with you.

We eluded to the fact that Eurorack has many uses; these can range from the most basic scenario of providing a single synth voice, to acting as an effects processor, with the ability to sample, capture and manipulate audio in realtime, or as a stand-alone system which is akin to a good old-fashioned groove box. Your direction of travel will be informed by the music you produce, but Eurorack has the uncanny knack of delivering the odd mishap and mistake, which might also dictate your next musical direction.

As a form of music technology, Eurorack’s is very much linked with the musical past – although not perhaps as far back as you might think. The format was brought to prominence in the mid90s by German inventor and musician Dieter Doepfer, with the release of a fully-formed system called the A-100. This module configuration became the standard for the format we now call Eurorack. Drawing upon the modular synth traditions inspired by synth pioneers such as Bob Moog, the Eurorack form is compact and slightly smaller than most previous modular formats, with a module height of 3U (133.4mm), and a horizontal unit measured in HP (horizontal pitch) which equates to 5.08mm to 1HP. Many modules will be 4, 6, 8 or 12 HP in width, with some even wider. This allows Eurorack users to decide on modules, based upon space available. Many modules can feel condensed, with the plus-point being that you can squeeze large amounts of functionality into a small space.

Power and control

Power is also standardised, with modules being connected to power boards which are normally fitted into Eurorack cases. It’s not uncommon to find power boards with around 12 connection points per row of modules, which is an indicator of how many modules you might be able to squeeze in a line. The system itself runs on low voltages, normally powered via an external 12v DC power supply.

A word of warning here! Some power boards will allow users to connect modules incorrectly, with the positive and negative polarity the wrong way around. Some companies get around this with the use of ‘shrouded headers’, which mean that modules cannot be connected incorrectly. However the most commonplace mantra for all Eurorack users is ‘Red Stripe Down’ , which relates to the negative connection being indicated by a red stripe, which will normally also run along the power connection ribbon cable. Keep the red stripe low and you’ll not blow any of your modules; however if you do find yourself with a module that goes up in smoke, it’s normally an easy and cheap fix, by anyone who can solder efficiently.

Another throwback to music technology’s past is with the control of the Eurorack. While it is the ideal to connect your modular via MIDI, the format itself relies heavily on Control Voltages (CVs) and Gates. This was the convention pre-MIDI, as a simple and effective way of triggering notes using a gate to dictate note length, and CV for determination of pitch. Helpfully, Eurorack conforms to the standardised 1v per octave format, with most modules allowing control over five octaves, with some allowing up to ten octaves. The CVs may also be employed elsewhere in the system to do other cool things, such as real-time modulation.

But why?

All this talk of formats is probably not exactly selling the prospect of modular, so let’s go back to the initial question; why go modular? Think of Eurorack as a system, in which you hold the control. You can start with a basic system and add to it on a regular basis to introduce different sounds, tones, functionality and processing. While it is electronic, it’s an organic process, as many modules can help inspire through their ability to generate notes and sequences randomly. It’s also possible to employ onboard and external sequencers, allowing programming of music within the modular, which can then be synchronised with your computer, either to run alongside or capture for further enhancement within your DAW.

However, for us, the biggest coup for modular is the physical concept of signal flow, where you literally have to pick up a patch cable and route your sound or signal. There’s nothing quite like that element of control, which is so satisfying, a little like the musical equivalent of Lego bricks!

In the spirit of this launching point, we’re going to start with the absolute basics and build a single voice mono-synth, paying particular attention on how we connect it to our existing computers and hardware, and start making cool sounds!

What you need

Let’s begin with the computer side of business; in order to connect any external synth, you’re going to need two points of connection, namely MIDI and audio.

In recent years, the humble 5-pin MIDI plug has been usurped by the introduction of USB MIDI connections. However we are looking to take advantage of CV/Gate for our Eurorack, and at the present time, there is more choice for conventional MIDI to CV/Gate convertors than anything which will accept a USB connection. Hence, the predictability and reliability of a standard 5-pin MIDI connection emanating from your host computer will always be a good stalwart. It’s stood the test of time for good reason.

If your computer lacks a MIDI output, the iConnectivity Mio (£39 – is a cheap, simple solution, for both Mac and PC.

While the MIDI interface will provide triggering from your DAW, we’re also going to need a way of listening and monitoring, and this will probably be easiest via an Audio interface. Eurorack systems tend to work with mono signals, but depending on where your modular takes you in the future, stereo signal processing with Eurorack is becoming more commonplace, hence it would make sense to think ahead.

As we’ll want to monitor the Eurorack, with provision for both playing alongside your DAW and recording it into your DAW, a good quality audio interface is always a sound investment. One such reliable workhorse is the newly updated Audient ID14 Mk2 (£199, which will comfortably provide Stereo in and out, along with a pair of excellent mic pre-amps, in a box which looks stylish on a desktop.

Another ideal solution is offered by Steinberg; the UR22 Mk2 (£119,, which will provide both MIDI and audio capability in a single box. Ignoring the Steinberg branding, this is an interface which was actually co-developed with Yamaha and will work with both Mac and PC, and with any DAW. A newly updated ‘C’ version of the UR22 now provides USB C connectivity, which will be of interest to MacBook users, where the dominance of this newly styled connector has become the norm.

Armed with your audio interface, it will be important to install any associated software, in order to get the most from the hardware. This will include the ability to monitor latency-free, keeping your Eurorack setup firmly in sync with your DAW.

Turning our attentions to the Eurorack setup, you’ll need to get yourself equipped with a number of basics to make a noise.

Casing the joint

The first components to consider could be regarded as the most important; the case and the power!

If you are nervously taking your first tentative steps into the Eurorack domain, the best advice would be to buy a case with power included. It is possible to buy cases without power, and you can buy the power elements separately, but with several off-the-shelf solutions available, it makes sense to keep things simple to begin with.

Cases come in various shapes and sizes. There are certain sizes which are fairly standard, always dictated by the number of rows and how many HP are on offer. As a starting point, two rows of 84HP, 104HP or 126HP should serve you well, but be prepared for things to fill up, at which point, you can expand with a second case, or buy something bigger.

In terms of the shape, the most common case is known as a skiff, and is designed to sit nicely on a desk or tabletop. If you think you might want to be portable with your Eurorack, cases are available with lids, designed to be easy to carry around. There are also plenty of more bespoke cases available, which offer greater size and proportion, and will be worth considering if you think you’re going to catch the Eurorack bug.

Time to module up!

Now to the exciting bit, with the modules that are going to form your signal path and generate some sounds.

As these are our first steps, we’re going to keep it simple and examine a basic system, much like a hardware monosynth, but with greater flexibility.

The starting point is the oscillator; the argument between analogue and digital continues to rage, even in Eurorack circles. However, the reality is that it simply doesn’t matter, as long as you are getting the sound that you want. Many larger Eurorack systems benefit from a blend of the two together, and certainly, digital oscillators will offer more functionality, as a rule. Analogue oscillators might sound slightly fuller in tone, in certain scenarios, but will offer less tonal contrast in initial waveform, whereas digital oscillators could contain many examples of traditional and more complex waveforms.

As we are keeping things subtractive in synthesis style, the next port-of-call will be some form of filter. These are also available in analogue and digital formats, and again, any argument is null and void, because both have their strengths and weaknesses. Analogue could offer degrees of impurity, which will offer that classic 70s synth sound, but could equally add some impurity to a digital oscillator. Similarly, you might yearn for a very clean and controlled sound, in which case a digital filter will offer superior accuracy with a clean tonal centre.

Our synth signal will need amplifying with a Voltage Controlled Amplifier (VCA), which would normally be linked to an Envelope module. The VCA will also work in a stand-alone mode, if you simply want to create tonal drones, but can importantly be linked with an envelope, if you want to trigger your sound like a conventional synthesiser.

Armed with these four modules (oscillator, filter, amplifier and envelope) you’ll be able to get going sonically, but you’re going to need other utility modules for linking to your computer for MIDI and audio. As we’ll be triggering from the computer, we’ll need a MIDI to CV/Gate convertor, which can be housed in the Eurorack, or purchased as an exterior box. It will also be exceptionally useful to have some form of audio output module, which could be considered the volume control for the Eurorack system.

There are also plenty of modules which are designed with modulation in mind, such as LFO-style modules. These can help to create vibrato and undulation effects, which will create movement in your sculptured sound. Not vital at this stage, but you’ll want to consider them as your system grows.

Analogue VCOs

Doepfer A-110 Standard VCO £129

From the company that started the Eurorack revolution, this basic VCO delivers four independent outputs of classic analogue waveforms. It’s a good entry-level VCO module, designed with a sensible price tag to get the novice started. It’s also available in either silver or ‘vintage’ black panel colours.

Studio Electronics Oscillation £249

This superb-sounding VCO is a flexible analogue oscillator, offering four classic subtractive tones, each with their own individual output, or the ability to sum them together in a mix. Furthermore, it’s equipped with a square wave sub oscillator, making it a huge-sounding starting point, for any classic subtractive-based synth sound.

AJH Synth Minimod VCO £260

The Minimod VCO is a transistor core oscillator which faithfully recreates the osc circuit from the original MiniMoog synth. It is also equipped with four independent waveform outputs, which include the legendary Sharktooth waveform, a staple of the original MiniMoog. This sounds amazing alone, or combine with other VCOs for that enormous phatt effect!

Digital oscillators

ALM Busy Circuits MCO £139

The compact MCO offers great sound and affordability, in a compact module format. It’s capable of morphing from one wave to the next, using the process known as wavetable, but is also equipped with a dedicated sub-oscillator output, in order to shore up those thundering bass sounds. It’s got a slight digital crunch in its tone, lending itself well to contemporary production styles.

Mutable Instruments Plaits £199

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