Toronto, Ontario, Canada

Modular synthesis intro, part 1: What is it?


My mother asked me to explain what I'm up to in one sentence, for inclusion in the annual Christmas Letter, and I said that I'm making electronic musical instruments. That's a pretty good summary as far as it goes. But people often want more detail on what modular synthesizers are all about, and this is the first of several postings I'm writing so that I can have a place to which I can direct the curious. It's largely based on a series of postings I made in my personal Web log about a year ago; the version here will be updated a bit to take into account subsequent developments in the modular world.

Polivoks synthesizer

Synthesizers are machines that make music. In a typical synthesizer - especially if it's based on analog technology - there will be many different subsystems connected together. Maybe an oscillator creates a sound, a filter adjusts its timbre, envelope generators and low-frequency oscillators produce control signals, and voltage-controlled amplifiers use the control signals to modulate the audio. Digital synthesizers often implement these functions as software components instead of physical hardware, but there will still be some kind of division into separate functional blocks that are connected together.

Subtractive synthesis patch

So: the business of North Coast Synthesis Ltd. is that of designing, building, and selling some of the modules for systems like this. I don't sell a complete line. To use my modules, customers also need to have other modules that I don't make, as well as the basic rack system for them to fit into. But my modules are designed to work with those from other manufacturers to form a complete system. I also sell do-it-yourself kits, allowing electronics hobbyists to assemble their own modules to my designs. And the designs themselves are freely available on the Web, to make possible modification and servicing by people other than myself.

Some history

As soon as electrical technology existed, people were applying it to music. Electric guitars date from the 1930s (depending on your definitions), as do Hammond tonewheel organs. Both of these are electromechanical instruments: the sound is born in a mechanical form and then translated to electrical signals for amplification and processing. Academic theorists started working on the ideas behind music that would be intended for purely electronic realization, starting in the late 1920s, and the "musique concrète" work from the 1940s into the 1950s put those ideas into practice.

Some of this early stuff used repurposed electronic laboratory equipment, which remains an inspiration for the look and feel of modular synthesizers even today. This kind of equipment often came in the form of rack-mounted modules, and when people started building machines specifically for the purpose of music synthesis, it was natural to build them in a similar form factor.

Bob Moog's was the first commercial modular system, in 1965. Don Buchla's, 1966, was also hugely influential. The Moog and Buchla rack standards are still in use today, though the original modules for them are no longer in production. These two systems came to typify what have come to be called the "East Coast" (Moog) and "West Coast" (Buchla) artistic approaches - my own company name of North Coast deliberately referring to those terms.

Switched-on Bach (W. Carlos, 1968) was performed on a Moog modular system, with a great deal of painstaking recording work. The synthesizer could only play one note at a time, so it couldn't play Bach's polyphonic compositions in real time. Instead, it was done by multitracking, recording one line at a time and then mixing them down. On top of that, the synthesizer's pitch drifted with temperature variations (a common problem with analog synths of the time) and so they had to frequently stop, retune it, and later assemble the best-tuned segments from the recording. But this album was a hit, and a great advertisement for modular synthesizers and synthesizers in general to the popular music community.

Modular synthesis experienced a wave of popularity in the 1970s. Groups typically described as "progressive," "new wave," and "psychedelic," got a lot of use out of these instruments. Some well-known modular users of this era included Emerson, Lake, and Palmer; Tangerine Dream; and Kraftwerk. After the 1970s, modular synths were replaced by integrated keyboard synths, first analog and then digital; these were easier to play, cheaper, more portable, and thus more practical for working musicians. The classic synthesizer sounds of the 1980s and 1990s are the sounds of non-modular keyboard synths.

Modular synthesis experienced a second wave of popularity in the late 2000s to early 2010s, largely among hobbyists and primarily involving the Eurorack system (smaller and electrically more modern than the Moog and Buchla rack systems; introduced by Doepfer Musikelektronik in 1995). My assessment is that many of the hobbyists in this second wave were people who had admired the modular systems of their favourite bands as teenagers in the 1970s, dreamed of one day owning equipment like that themselves, and the second wave was when those people reached the stage of life and financial security when they could finally make the dreams real.

Small Eurorack synthesizer on a hotel desk Doug and Dino, with Keith Emerson's Moog Part of a large Eurorack installation at FiveG, Tokyo

Today, the fad is wearing off. There is some contraction in the market, and we'll see some of the smaller and less serious players drop out, but at the same time, the people still remaining in the modular-synth hobby are the serious ones who will be here for the long haul. Professional musicians who use modulars are often those working in EDM genres; hobbyists are all over the map. Modular synthesizers are often used in sound design for movies and video games. There is also some interaction with the still-growing "maker" hobby electronics movement. Synthesizer electronics is a nice way to learn and apply general electronics skills. The focus on serious hobbyists is a big part of my own company's strategy.

I think a case could be made that very much of present-day modular-synth music is actually folk music, because folk music can be defined as the music ordinary people who are not professional musicians make for their own enjoyment. However, more than one aspect of that assessment would be controversial, and the music usually sounds nothing like what you would find in the "folk" section of a record store.

An example patch

Real-life musical sounds are often constructed by starting with a sound source that has a lot of harsh harmonics and them removing some of them to create a desired timbre. For instance, a person's vocal cords produce a harmonic-rich, only partially pitch-controlled, series of impulses, and then their throat and sinuses filter out much of those, leaving the frequency bands that define a vocal note. Similarly, a saxophone's reed produces an unmusical noise covering many frequencies at once, and the body of the instrument under control of the keys removes all but the desired frequency components to create a note. With a guitar, the pitch control is applied to the sound source (the strings) but then the timbre comes from the guitar body's selective attenuation of certain frequencies - and often distortion added by the amplifier, in the case of an electric guitar. Subtractive synthesis, typical of the "East Coast" Moog-style synthesizer sound, follows the same general plan of starting with a signal that contains many frequencies and then filtering it to shape the sound.

Sample patch

Above is a typical patch, as rendered by ModularGrid. (Click on it, or any of the thumbnails in this article, for a larger view.) It's actually the same patch for which I gave a block diagram earlier; a fairly typical subtractive synthesis patch.

At the left, there's a USB/MIDI to modular interface module. Someone could plug a MIDI keyboard into that to control the synthesizer. Then "control voltage" (representing pitch) and "gate" (representing the state of a key being pressed or not) signals go into a multiple module, which is a simple cable splitter. The gate signal connects to the inputs of two MSK 012 Transistor ADSR envelope generators (Attack, Decay, Sustain, Release); these particular modules are my own design, but the general concept of an ADSR envelope has long been standard in electronic music. The envelope generators create control voltages that mimic the typical pattern of volume or harmonic content in a note on an acoustic instrument: an initial burst (A - attack), then backing off (D - decay) to a steady level (S - sustain) and then falling away to silence (R - release).

Next on the right is an LFO (Low Frequency Oscillator) module, which you may notice has no inputs. This is also one of the ones I designed, an MSK 010 Fixed Sine Bank. There are many LFO modules on the market, but one advantage to this one is that it generates eight independent outputs, for modulating different things in a large patch without forcing them to synchronize. The LFO generates a continuous slowly-varying control voltage, which becomes an input to the VCO (Voltage Controlled Oscillator) module, next in line. That oscillator also takes a pitch input through the multiple from the MIDI interface. As a result: the pitch of the key pressed on the keyboard selects the main pitch of the oscillator, but that pitch will vary or waver at a slow rate controlled by the LFO.

The signal taken out of the VCO is a sawtooth wave - a harsh, buzzy timbre with many harmonics. That is fed into the input of a low-pass filter (LPF, Low Pass Filter, or VCF, Voltage Controlled Filter), which chops off most of the harmonics for a more mellow sound. In the example I've used another of mine, the MSK 007 Leapfrog VCF. VCFs are another category in which there are many different products available from different manufacturers; the main selling point for mine is that it sounds different, because of a much sharper filter cutoff than most competitors. The filter also takes as input the same pitch-control voltage used by the oscillator, so that it can track, producing a timbre that doesn't vary much as the player chooses higher and lower notes on the keyboard. But it also takes a modulation input from one of the ADSR envelopes. So when the player first presses a key, the ADSR produces a relatively high voltage and the filter allows through a lot of harmonics. Then later in the same note, the ADSR's voltage is lower and the filter lets through fewer harmonics. The result will be notes that start harsh and then become more mellow - a typical sound of both acoustic and electronic instruments.

But so far nothing actually turns the sound on and off; this patch so far will play continuous notes at whatever pitch was most recently used, even after the player has released the key. The last step in the patch is a VCA (Voltage Controlled Amplifier) controlled by the second envelope generator. In this case, the VCA is built into the filter module; they are also available as separate modules. At the start of a note the envelope generator produces a burst of voltage which causes the VCA to "open" and let through the signal. Over the course of the note the control voltage changes and so does the volume. At the end of the note, after the decay phase, the control voltage drops to zero and the output of the VCA fades away.

This patch is certainly usable as it stands, but part of the fun is that it can be changed. For instance, someone might connect another output of the LFO to a different parameter on the oscillator, changing the way the sound varies over time. With a larger system, one could involve more than one oscillator, or set up a more complicated control scheme with the envelope generators.

Do you play it with a keyboard, or what?

There are many ways to get the notes into the machine. Keyboards are popular. There are keyboard controllers that produce control voltages suitable for plugging directly into a modular. There are also MIDI interfaces allowing the use of a MIDI controller, which could be a keyboard, some drum pads, a breath controller, or something weird - or it could be a computer. If you want to control the modular from a computer, there are USB-MIDI modules that can plug the computer directly into the modular and appear as a MIDI interface to the computer without actually using bulky MIDI cables in between. There are modules (a company called "Expert Sleepers" specializes in these) specifically designed for interfacing to DAW software, with a proprietary interface through the sound card backed by software plugins on the computer side. There are also sequencer modules that fit into the rack and can be programmed using front-panel controls without a separate computer.

In some styles of music there may not be much playing of notes as such at all. Instead one might design a sound that changes over time and just let it run, recording what comes out. That's popular in some ambient styles. Some modular users are very interested in what they call "generative" music, where the synthesizer is set up to create its own melody without direct human input. A human being might then have some more abstract control, perhaps adjusting the mix and timbre in real time while the machine is generating notes.

In a lot of my own music, I first write a score in music notation with a computer, then have the machine play it through the MIDI interface while I manipulate the controls of the synthesizer for expression. This is a little bit like what people used to do with the better class of player piano, where the piano roll specifies the notes but a human operator controls other aspects of the performance.

Playing a modular synthesizer is sometimes called "wiggling" (because the player wiggles the knobs on the machine) and the people who do it, "wigglers."

Where does the output go?

The modular synth produces sound as an analog electronic signal. To hear it, you need to connect it to something that can change that signal into sound. If you have a mixing board, you can usually plug the synth directly into the board, as you would with line-level outputs from other equipment. The normal modular level is hotter than line level, but with a little care, it's usually possible to adjust the two devices to communicate with no more interfacing than maybe a plug adapter.

Beyond that, you can attach speakers, headphones, a computer's sound input, or anything else that can accept an analog audio signal. Some of these options may require an interface module of some kind, and of course there's a wide range of those available. There are modules consisting of speakers that fit directly into the synthesizer rack, but I don't think they're very popular, because they take up a relatively large amount of rack space and it's usually at a premium. Most people plug the synth into external speakers of some kind.

Can you plug a guitar into it? Is it kind of like guitar pedals?

Sort of. Guitars and guitar pedals run at different electrical signal levels from modular synthesizers, so you can't just freely connect them. You need interface modules designed for it, to boost the low instrument level up to the very high modular signal level, and to attenuate in the opposite direction. But such modules certainly exist.

My impression is that people who think they want to do this sometimes end up disappointed. "I want to process external signals, like from my guitar!" and "I want to use my existing collection of pedals with the modular!" are often high on new users' lists of things they want to do, and I don't see it actually going on very much among more experienced users. I think it's usually more fun to treat the modular synth as a separate instrument, which you might play along with other instruments without it becoming part of their signal chain. But that's a philosophical point on which others might differ, and from a technical perspective: yes, it's definitely possible, and people do it. As for similarity: yes, it's not identical but is kind of like guitar pedals. And there's a lot of overlap. Many people are interested in both.


Modular synthesizers are electronic musical instruments whose functional blocks are split into separate functional units that users can mix and match. They were historically important in the development of electronic music; fell out of use as cheaper and more convenient integrated synthesizers became popular; but have had a recent resurgence among hobbyists. I'm making modules for use in such systems.

Continue to Part 2 of this series.

Free MIDI software rundown || Modular Gift-Giving Guide 2017

MSK 015 Quad VCA SDIY Kit

MSK 015 Quad VCA SDIY Kit

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Thank you for writing all of this info, very helpful!

Patrick from Columbus OH
Patrick - 2021-12-06
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