Introduction to modular systems

Hello to you! If you are reading this guide, you are about to embark on the magnificent adventure of the modular synthesizer. This little guide, without any pretension, is made for you! We will first try to orientate you in this jungle filled with rare and crazy species and try to help you determine your tastes and expectations. The aim of this guide is to allow you to have fun and enjoy yourself while working on modeling your sound.

So without further ado, let’s get started!

What is a Modular Synthesizer?

The Synthesis Voice

A modular Synthesizer, theoretically, requires only one module to emit a sound: the VCO (Voltage Controlled Oscillator). You will nevertheless quickly need other modules, which we will call “basic”, to be able to really start playing your instrument. Here is a list of the modules that your modular system could contain:

  • Voltage Controlled Oscillator (VCO): Generates wavefoms more or less rich in harmonics.
  • Voltage Controlled Filter ( VCF): Filters the harmonic content of a sound.
  • Envelope Generator (EG): ADSR for “Attack”, “Decay”, “Sustain” and “Release”.
  • Voltage Controlled Amplifier (VCA): Allows to modulate the amplitude of a sound or a voltage.

For the latter, note that the letter A in the acronym VCA is often associated with the term “Amplifier” but that electronically speaking it should rather be called “Attenuator”. But this abuse of language is so common that it should not be a problem for you to understand.

Six Flags over Modulars

The main attraction of the modular synth is to differentiate itself from the classical synth, with a so-called fixed architecture, by allowing the placement of the different modules in the order one wishes on the signal path. To facilitate the development of a balanced modular system, the modules can be classified by functional families (non-exhaustive list):

  • Audio Generators: VCO, noise generator, sample player.
  • Processors: VCF, VCA, ring modulator, slew limiter.
  • Modulators and CV generators: ADSR, LFO, sample&hold, sequencer.
  • Utilities: mixer, offset, inverter, attenuator, switch, multiple.
  • Effects: reverb, delay, phaser, flanger, chorus.
  • Controllers: joystick, touch surface, keyboard, ribbon.

Note that some modules can be found in several families and fulfill several functions, different from their primary function. Thus a VCO can also be an LFO (and vice versa), an auto-oscillating VCF can serve as an audio source. In order to create a coherent and balanced modular instrument, it is essential to include elements of the first 4 families. Families 5 and 6 are optional, but nonetheless interesting for cases where the targeted system must be autonomous.

Formats and Power Supplies

In modular as in many other fields, there is a multitude of offers for a multitude of demands. First of all, it is advisable to make a clear and precise distinction (when it is possible) between the various formats which animate the market. What we call “format” in the field of modular synthesis corresponds in reality to two things:

  • A front panel size (and by extension jacks size)
  • A power supply voltage

At first sight, the size of the front panel may not seem very important when you start talking about modular synthesizers, but it is in fact often this first choice that will be decisive in the orientation of your future system. This choice will have to be made in relation to the space available in the studio and according to whether your modular will be portable or not. It is therefore important to make the right choice from the start! Generally speaking, we distinguish three formats:

  • The 3U Eurorack
  • The 5U
  • Other proprietary formats

Height is measured in Units (U), 1U = 44.45 mm = 1.75 inches

For the width, different terms are used depending on the format:

  • In Eurorack, we speak of “hp” (horizontal pitch) with 1hp corresponding to 5.08mm.
  • In 5U, we also speak of “U” to determine the width of the modules. However, there are two standard widths:
    • The MU width for Moog Unit (Moog, Synthesizers Dot Com, etc.) : 1U width = 54 mm
    • MOTM width (Synthesis Technology, Oakley Sound Systems, etc.): 1U width = 44.45 mm

3U Eurorack

Roughly speaking, the 3U Eurorack format is the most common. The modules are very compact, the patch cables are mono 3.5mm mini jacks. This is without any doubt the most active format at the moment. New modules and new manufacturers are being continuously introduced and ModularGrid is now counting over 9000 modules. Moreover, the second-hand market is very active, a good point for anyone who is a bit patient and wants to build a system for not very expensive. 3U Eurorack format works with +12/-12 Volts and some modules require +5V to supply their digital circuitry or tube heater.


The 5U format takes more space but allows a better ergonomics. This format uses 6.35mm diameter jack cables. It is originally rather oriented in a “classic” spirit (understand East Coast) à la Moog modular, even if new modules and original systems are also starting to appear. The 5U format generally works in +15/-15 Volts with a +5V necessary for some modules (quite rare).

Proprietary formats

Then there are manufacturers like Serge, Buchla or Wiard that are making modules of other format sizes like 2U, 4U or even 6U. These modules are generally more oriented towards West Coast synthesis and for the most part are much more expensive. It is therefore perhaps not with these formats that the beginner in modular should start. These systems also have the reputation of being much more complex than the “standard” formats, with a much steeper learning curve. Those systems all work with their own voltages +12/-12V, +15/-15V for others and some even require +18V or 9V.

Whatever format you choose, the market is so flourishing that you will have no trouble finding the basic modules you are looking for. The choice will be made first of all on the more or less advanced functions of the modules, their sound quality, the approach, the visual aspect, the ergonomics and of course their cost.

Brief History of Modular Synthesis

East Coast or West Coast?

These terms come up here and there in the course of many discussions about module formats. If this term doesn’t mean much nowadays, you should know that it actually represents a (philosophical?) approach to modular synthesis as it was set up by the pioneers of the time, namely Donald Buchla and Robert Moog.

At the end of the 60’s, the first synthesizers (modular, needless to say) were born in the USA. Moog began his work in Trumansberg, New York while Buchla got his start in Berkeley, California — hence the designation of East and West Coast. The approach of the synthesis by the two men, even if on the technical level is not very distant, is completely differentiated by the very concept of the instrument with its controls and the use for which their modules are intended.

In the early 70’s, Bob Moog saw his order book swollen by musicians wanting to take advantage of the new sounds that these machines offered at that time. So, at the request of keyboard players, he developed a system allowing to control the oscillators with a keyboard. The ancestor of the Minimoog was born.

Don Buchla, on the other hand, worked at the request of a musician (Morton Subotnick) with a radically different approach and developed a series of modules such as Sequencers or Envelope Follower. Also, instead of a keyboard, Morton says that in order to make the best use of the Buchla 100 system, they had developed a touch-sensitive, pressure-responsive controller to trigger tape recorders/players.

The two schools were born. While the East Coast school of Moog synthesizers were used extensively for tonal music. The West Coast school, led by Buchla and later Serge, put more emphasis on the experimental side of electronic music and designed their synths accordingly.


Practical differences

Moog (and by extension East coast) systems are based on the classic format: VCO – VCF – VCA – EG. A waveform rich in harmonics is sent from the VCO to the filter (generally a 24dB LowPass Filter) and is then sculpted in the latter. The envelope allows, depending on the keyboard playing, to act on the duration of the “sound output” through the VCA. We are talking here mainly about subtractive synthesis, by filtering superfluous harmonics.

Buchla systems are based on the addition of harmonics to poor waveforms (Sine, Triangle). Thus, generally a sinusoid is sent to a Waveshaper in order to add harmonics to it. The Buchla filter also exists but is traditionally designed as a 12dB BandPass. The VCA is finally replaced by an LPG (Low Pass Gate). We are talking here mainly about additive synthesis, FM and Dynamic Wave Shaping.

So why go modular ?

If you are here, you have probably already made up your mind about going with a modular synth. But for people that may have hard times making up their mind, I will give you an honest view on modulars.

Modulars are not cheap, sorry to start with bad news and talking money but you have to know that having a basic complete system will ask you to spend between 500€ and 1000€. But well, you can think of it as it is as expensive as a good guitar or a good amp. And with DIY kits and a small electronics knowledge, you can expect to lower that price. Remember that the investment is at the beginning, once you will have a small set-up, you will be able to add new modules once in a while.

In the case of Eurorack systems, with all the brands making modules comes lower prices, and with all that diversity you will be able to build your unique instruments. Every module choice will help you customize your rack, you will be able to mix analog and digital or modern and vintage modules.

With this flexibility, your rack can be used to shape sound like no other self-contained synth. Knowing more about the elements of synthesis and by experimenting, you will discover a new approach to sound synthesis with sometimes unpredictable results.

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