Modular Synthesis 101: A Guide to Eurorack Modular

Most people are familiar with the modern synthesisers. It’s likely if you’re reading this you’re a bedroom producer of sorts and have probably heard of most of the main plugins people use – Serum, Massive etc. Perhaps you’ve even got a controller for inputting and tweaking MIDI data.

Maybe you’ve seen some student union indie band equipped with a microKORG or you may be lucky enough to own an analog synth or two. Either way, the majority of people are familiar with the architecture of what we know as a synthesiser: oscillators, filters, amps, LFOs and envelopes.

At this stage it’s worth noting that if you are unfamiliar with any of these concepts, you should probably have a look at this beginners’ guide to synthesis.

When you purchase a synth the oscillators, filters, and amplifier are all hardwired into a particular order; sure, you can modulate them with the LFOs and envelopes but that’s really about as much flexibility as you’re afforded.

lHowever, the modern synth as we know it has not always been this way. It wasn’t really until the very early seventies that it came to be an all-in-one. Before the synth there was the modular synth.

The principle of modular synths was that you had a module that performed a singular function (or a limited number). So maybe a few oscillator modules, VCFs, envelopes, LFOs, sequencers, slew limiters, VCAs, ring modulators and other such exotic things.

A keyboard wasn’t even a necessary inclusion of early modulars; this would be an extra that was necessary to connect if you wanted to impress your friends playing Chopsticks (although Chopsticks would require loads of voices, and modular synths didn’t really handle polyphony that well).

Here’s Keith Emerson explaining it in a more eloquent manner than myself:

These monster synths are housed in huge cases and, to lay people, might look like something better suited to a laboratory rather than a recording studio but the flexibility and sonic possibilities are something than can go beyond that of a traditional synth.

Modular synthesis has been recently enjoying a revival of sorts through the Eurorack format, with big dawgs like Roland, Moog and even Waldorf (re)joining the party. So maybe it’s worth looking a little at the history and how to get started if you’re interested in delving into the modular world.

Why Modular?

Good question. Modular is great for a number of reasons, not least the flexibility of being able to re-patch your machine in nearly anyway imaginable can create sounds you might never have dreamt of using a mouse and keyboard. You can buy clones or filters from unobtainable synths, you can create huge stacked sounds not possible with plug-ins and you can improvise to your heart’s content.

In fact, modular synth collection is really like Lego for adults. Sure, you can buy the premade stuff and have it sitting on your shelf or you can really get inside something and combine modules from different companies, east and west coast, vintage and modern, analog and digital and build something totally unique that is never really the same twice.

Modular synthesis has a tonne of drawbacks and these often put a lot people off. Modular synthesis is hella expensive, there’s no doubt about that. Yes you can buy modules for as little as £50 but in reality, if you want some sort of functional system, you might need to put aside a few more of your hard-earned pounds than that.

For a start, before you’ve purchased your first oscillator you’ll need something to house your device, power supply and cables in. This can be as little as a £150 but for some even that’s enough to make them wince. To get a sound going you’ll need maybe three or four modules (more on this later) or a prebuilt system and these don’t exactly come cheap.

Modular doesn’t really do chords. Yes, polyphony is possible but it’s a pain in the ass and expensive. If you’re interested in playing chords I would really suggested either sticking to plugins or saving up for a decent poly synth. To reiterate, it is possible but it’s not an easy route. And if that still hasn’t put you off, modular doesn’t really handle stereo that well either (however, there are some stereo output devices available).

East Coast vs West Coast

Long before the much-publicised Bad Boy and Death Row Records row, there was Moog and Buchla. Trumansburg, New York’s Dr. Robert Moog (pronounced /ˈmoʊɡ/, or moge) is verging on a household name to most. From his legendary Minimoog to MoogerFoogers, Taurus to Theremins, and the Vocoder to the Voyager, Moog are not short on their historic music-making machines.

Before their ventures in keyboards Moog cut their teeth building furniture-like modular synths. Known for their playability and musical compatibility, these devices could be seen propping up the studios of Tangerine Dream, Giorgio Moroder, Hawkwind and Emerson, Lake & Palmer, to name but a few.

With a plethora of modules available, perhaps their best known is the much-sought-after (and regularly cloned) Moog Ladder Low-Pass Filter, which is to my knowledge the only patented filter. Buchla is a less familiar name. Started by Don Buchla in 1963 in sunny Berkeley, California, these machines were less about making music and more about creating sounds when psychedelia was in full swing.

The 200 series is one of more well known creations from Mr. Buchla. The modules it came bundled with were more esoteric than its east coast counterpart. Modules such as the Source of Uncertainty, Lopass Gate,  Function Generator, Spectral Processor and Kinesthetic Input are among the more sought-after and replicated devices.

There’s now some controversy about the ownership of the company with Don taking legal proceedings with the current owners, so keep your eyes on that.

If you’re interested in learning more about the history of modular synths I implore you to buy the I Dream of WiresI Dream of Wires. It’s a very comprehensive history of what came even before Moog and Buchla, right up to the eighties and modern day, and very much worth getting.

Loveable Format

Modular synths come in many different formats. The aforementioned Moog and Buchla are two but there are also other 5U formats like MOTM and Synthesiser.com, there’s EMS and Serge, Frac and probably some I’ve missed out. The one I really want to focus on today is the format that’s caught the attention of the masses: Eurorack.

Before getting into modules and companies, there are some great resources worth looking into (as well as this). Firstly is ModWiggler, which is a synth specialist forum, and basically the holy grail for all things modular. In my brief time there everyone’s been very friendly and there are tonnes of stickies on starting out and learning how to do this, that and the other so definitely invest some time lurking there.

The second is SoundOnSound’s excellent starter guide, which I read in their print edition back in 2011 and instantly decided this was for me. Tonnes of useful info about all the formats (again specialising in euro) and very well written and informative.

Finally, get a ModularGrid.net account (it’s free!). This is an html5 modular planner which is properly addictive, especially when starting out. You can build a hypothetical modular, see how much it costs, see its power consumption, plan which modules go where etc. etc.

Happy Endings

This guide is going to assume you want to pursue the Eurorack format. After much deliberation, this was the route I chose. A select few of my friends had small euro systems, so advice was easy to come by.

Euro is smaller than other formats, (generally) cheaper and more uniformed in terms of power and signal level. Also, there seem to be euro companies cropping up every five minutes (which may be a good or bad thing) so there seem to be a lot of new products available and plenty of innovation.

So, some boring things to start off with. You’ll need a case, or at least something to house your device in. There are two routes you can take: buying a dedicated encasement (like these by Doepfer or Eastwick Cases) or something like TipTop Audio’s Happy Ending Kit. I went with the latter as it was cheaper and could be housed within racks, of which I had plenty lying around. It also meant I could expand without buying another case.

Sonic State have written a very handy guide to low-cost cases. Read it here.

The Happy Ending Kit (or HEK, above) contains the rack in which you can mount your modules, a unit to power your modules and something to plug that into the wall. They retail at around £130 from most stores. There are other options but this is the one I chose.

HP Sauce

HP stands for horizontal pitch and is the unit we measure eurorack devices in. The TipTop Audio Happy Ending Kit is 84 HP wide which means you can fit as many modules that add up to that number in there.

For some comparison, the HEK comes with a power supply unit that is 4 HP wide (the silver device on the far right, named the μZeus). Some cases are 104 HP wide, some smaller. I thought 84 HP was enough for me to get started and build a basic device to get going.

Most eurorack modules are between 4 and 14 HP, with some as small as 2 and some as as big as 20 and larger. Most modules are an even number of HP but companies like Befaco, The Harvestman and hexinverter are known for odd numbered HP modules. If you have a 1 or 2 HP gap you can always buy blank panels to satisfy your OCD for filling space.

Getting Started

The first thing you need to think about is ‘what do I want my modular to do?’ It’s a profound question – you can build a basic monosynth, you can have something for live improvisation, something that focuses on generating sequences and patterns, an effects rack, something that manipulates signal or something that combines a little of all of these.

When I was starting out I wanted to first build a simple one-voice monosynth that did exactly what I’d expect of it; then, once that was done, I could expand by buying modules that performed routine functions. I wanted predictable sequencing with a little bit of uncertainty thrown in for good measure. I wanted to be able to get it to talk to Ableton but also take it out and have it as a standalone.

My first modules (bar the μZeus) were all made by Doepfer, who are like the Boss of the Modular world (the Boss owned by Roland, not some sort of hierarchical thing). Before I even had an oscillator I’d acquired a few ‘essentials’: VCAs and multiples. From left to right you can see:

• Doepfer A-138d Crossfader / Effect Insert Module (8HP)
• Doepfer A-119 External Input / Envelope Follower (8HP)
• Doepfer A-180-1 Multiple (x2, 4HP each)
• Doepfer A-124 Wasp Filter (8HP)
• Doepfer A-183-3 Amplifier (4HP)
• Doepfer A-131 Voltage Controlled Amplifier (exponential) (8HP)
• TipTop Audio μZeus Power Supply (4HP)

There are lots of reasons to start with Doepfer: they’re cheap, durable, there’s a tonne of selection and they do pretty much exactly what they say on the tin. Great for beginners:

I’d purchased some of these through EMIS Music (the UK’s leading Doepfer distributor) and some from eBay in a bundle (hence some choices I might not have made were they to be all purchased individually).

Later I purchased a VCO (voltage-controlled oscillator), White Noise/Random Voltage Generator, LFO, Ring Modulator and Envelope and it was starting to take shape as something of my own:

From there, I expanded into some different companies’ modules and started really customising it. But enough about me…

CV, Gate, Trigger and Audio

There are a few different signal types so it’s worth familiarising yourself with them to properly understand how to get patching. Audio is probably the simplest to get your head around: this is a produced sound that can be heard. For example, an oscillator produces audio signal, you plug that into the Audio In on a filter and there’s an output that produces the resulting, effected audio.

CV stands for controlled voltage and comes in a few different forms, too. If we want to modulate said filter, we can take an LFO or an envelope and plug their output (not an audio signal) into the CV control. This is a continuous signal that isn’t heard, but its effect is.

Gates and triggers are both binary signals that can be represented as pulse waves. Where as triggers are a short blip indicating clock divisions or triggering a drum machine, gates are note on/note off informing how long an envelope should stay open, for example:

Here we can see the note on information is the red dotted line, and note off is the blue. Audio signals are at an audio rate (20 Hz to 20 kHz) and can be heard as a sound in the form of an alternating current (AC) which has an audible frequency (pitch) and amplitude (volume).

CV signal is direct current (DC) and could be pitch information, an LFO, envelope or any other modulation source.

Gates are high when a note is depressed and low when it’s released. This would normally come from a keyboard rather than a sequencer.

In this example the trigger hits at the same time as the gate but is momentary. Triggers could also be plugged into a sequencer with clock information, but we’ll cover that in more depth another time.

Modules by Type

As mentioned earlier, it’s probably worth having at least a basic understanding of synthesis and signal flow before delving head first into modular world but it’s by no-means necessary as modular is a fantastic way to learn about synthesis if you’re just starting out. Let’s start out with some basics i.e. modules that are the same in the modular world as they are in the plugin world.

VCO (Voltage-Controlled Oscillator)

Sine, Triangle, Pulse or Sawtooth – you need a sound source in order to started shaping your sounds. One big difference between modular and what you might get in a plugin is that oscillators are always running: if you plug one into a mixer you’ll hear a sound, regardless of whether or not you trigger it (we’ll cover more on this later).

A number of companies make great oscillators: Doepfer, Pittsburgh Modular and MFB are among the cheaper options where as intellijel, Make Noise and Mutable Instruments offer some more interesting alternatives, albeit with a larger price tag attached to them.

VCF (Voltage-Controlled Filter)

Filters are common-place in modular systems. They work by removing certain overtones and harmonics from an audio signal. The usual suspects can be found here, low, high and band pass, as well as less common filter types like all-pass and comb.

All filters contain different components so will have different sweet spots and react to different modulation sources, especially with the resonance cranked up.

Doepfer offer a huge range of filter clones*, as well as Koma Elektronik, Malekko and Analogue Systems offering popular alternatives.

Envelopes/Function Generators

You should be familiar with envelopes if you’ve dealt with synthesizers in some capacity before: attack, decay, sustain and release parameters can shape our amplitude, pitch, filters and really just about anything that has a CV input.

Function generators are a name given to loopable stages of an envelope, so an AD or AR envelope that loops could be described as a function generator. Make Noise’s MATHS is probably the Don Corleone of this genre, being so flexible and multifunctional. Worth reading more about it than me trying to describe its many talents:

LFO (Low-Frequency Oscillator)

…or LFOs, as they’re abbreviated, are used as modulation sources to control parameters such as amplitude, pitch, filter or (like envelopes) just about anything. Typically they operate below 20 Hz but some can run into audio rate for frequency modulation effects.

Look out for dual LFOs, LFOs with phase restart/cycle retrigger, ones with voltage controlled frequency modulation, noise and random waveforms etc.

VCA (Voltage-Controlled Amplifier)

Seemingly an uninteresting module at first, these things are actually gold dust as probably everyone on ModWiggler will tell you. Really it’s an amplifier that we can use to control the volume of our patch with an envelope (via a keyboard or a sequencer) or an LFO but it’s really so much more than that; I’ll try and cover it more another day.

VCAs come in linear (for CV) and exponential (for audio) forms. This refers to the curvature of the slopes that modulation sources would provide. You don’t have to stick to this recommendation, though, and look out for VCAs that handle both like this Doepfer one.

MIDI to CV

If you want to play your modular like a keyboard, you’ll need to interface with it via MIDI. There are a few of these on the market; I opted for the Kenton Solo (as I had the desktop version already) but Doepfer, Pittsburgh Modular and Mutable instruments all offer similar capabilities, with Expert Sleepers taking it a step further with their desktop software.

The two outputs of a MIDI to CV module are pitch CV (1V/oct as opposed to other analog synths that might use hertz per volt) and gate. The former connects to oscillators as well as key tracking on filters whereas the latter trigger envelopes. Additionally, you can take clock information from a DAW such as Logic or Ableton and control sequencers – more on this later.
Read more about CV and gate on the Wiki.

Drum Modules

Drum modules are not something I’ve gotten into. Personally, I prefer to keep this in Ableton but that doesn’t mean it’s not something I’ll explore more in the future.

TipTop Audio offer decent clones of the Roland TR series of modules while hexinverter have some more customisable options. Usually drum modules require triggers from sequencers. Lately, Bastl Instruments have entered the Eurorack market with an incredible looking drum system:

Sequencers

A big top topic, which will be covered in in more depth in later articles. There are basically two types of sequencers so, like our MIDI to CV modules, we can get sequencers for CV and sequencers for gate (or triggers).

Pitch sequencers normally have rotary pots and come in 4-, 8- or even 16-step variations. I have a trusty Pittsburgh Modular Sequencer but Make Noise, intellijel and Xaoc Devices all offer more advanced alternatives.

Gate or trigger sequencers work by outputting positive or negative signals such as +5v(olts) or 0v at regular intervals, to either trigger a drum machine or an envelope. These can range from simpler devices, like Doepfer’s A-160 or the 4ms clock dividers and multipliers, to Euclidean sequencers like the Rebel Technology Στοιχεῖα or ALM’s Pamela’s Workout:

Quantizers/Slew Limiters

Two separate things I thought I’d bundle into one, here. Quantizers will lock controlled-voltage signals into pitches; by default, they’ll chuck out a series of voltages that aren’t necessarily in tune. By far my favourite quantizer is the µScale by intellijel, but the Expert Sleepers Disting is also great (for many other functions, too!):

Slew Limiters are what most people might know as Glide or Portamento. Sometimes sequencers have this built in. I think the best value for money is the Pittsburgh Modular Toolbox as it does a few of the next functions too…

White Noise/Random/Sample and Hold

White Noise is found on lots of synthesisers. It’s used to synthesise hi-hats, snares, riser FX and to dirty up leads and basses. Because it is every frequency at equal amplitude, it’s the closest thing we can get to random in the analog world. The Doepfer A-118 is a good shout to do this, as is the Toolbox mentioned above which also does inversion (more on this later) and Sample and Hold.

Sample and Hold takes an incoming signal and samples it as a given interval (determined by a rate, normally a pulse wave). It’s the typical R2D2 sound or bleepy-bloppy sound a lot of people associate with 50s sci-fi sound design.

N.B I tried to knock up a diagram of Sample & Hold in Illustrator but it was harder than I thought so I’ll dedicate something to it in more depth another day.

Logic

If you’ve had any experience with computing or circuit design you might have come across logic gates, which can include AND, NOT, OR and XOR processes. These (usually) combine gate signals from different sources and output something whether or not the logic is true. This is useful for creating longer pieces of music and turning on and off sequencers.

This is best explained by Professor Brailsford from the excellent YouTube channel Computerphile. Note logic is normally discussed with binary numbers 1 and 0, which equate to on and off. For our purposes, when a note is on the gate has an output of 1 and when the gate is off the output is 0:

Here’s a handy diagram explaining the different types of logic gates:

Ring Modulation, Waveshaping and other Effects

Like guitar pedals, the modular world is not exclusively sound sources and modifiers: you can have sound affecting modules, too.

Ring modulation creates metallic sounds by multiplying two frequencies together before outputting the sum and difference and is responsible for the Daleks’ voice. At lower rates it can sound like tremolo (amplitude modulation) and at more extreme values you can achieve extreme atonality. There are loads of the market, so do your research first.

Waveshaping is sort of asymmetrical distortion found in lots of modular that works by folding and clipping parts of the cycle in on themselves. There are a few options by Doepfer but intellijel and The Harvestman are among the more popular:

Other effects that are worth considering for your machine are spring reverbs (Doepfer and Befaco are a good shout), delays (the SnazzyFX’s Wow and Flutter and Make Noise Echophon are pricey but great-sounding), distortions (like Metasonix and the WMD Geiger Counter) and phase shifters:

Hat tips also go to ALM’s S.B.G that allows you to interface with guitar pedals or rack units.

Multiple

Multiples are super useful modules, taking a signal and duplicating it. This is great for taking an LFO’s output and sending that to a filter, VCA and phaser, for example, or taking pitch CV and sending it to three oscillators. For these reasons, it’s worth planning at least a couple of multiples into your system.

Gate, triggers and other CV signals can be sent from passive multiples (ones not plugged into the power supply) whereas pitch CV needs to be multiplied through a buffered multiple (such as intellijel’s or this one from 4ms).

Here’s Richard Devine demonstrating Make Noise’s Teleplxer:

Input/Output and Mixers

As the title suggest, these modules interface with your system. Outputs can be audio interfaces or just attenuators to keep the signal from getting too hot before it hits a mixing desk/soundcard. Inputs can take guitar or synthesisers and process that with your modular.

Mixers are useful not just for blending audio signals together but mixing CV signals too. You can also amplify or attenuate CV to get desired effects.

I like my Trouby Modular Jack 8 for interfacing with my patchbay, the Doepfer A-119 or Xaoc Devices Sewastopol is a good shout for for input device. There are far too many good mixers to mention in these pages.

Attenuators/Inversion/Offset/Polarizers

I will cover these sorts of modules in greater depth at another opportunity. In principle they are ways of modifying CV, attenuators turning it down, inverters inverting it (surprisingly!), offset modules add a certain amount of voltage to some and polarizers are a little more complicated.

Doepfer’s A-183-2 is a one-stop shop for three of those four functions, while the Toolbox (mentioned in other sections) does inversion as well as sample and hold, white noise, slew limiting and inversion.

Where to Buy?

If like me you’re starting out with a Doepfer system, EMIS is a really good place to get your first few modules. Andy is very helpful and answered many emails from me before I committed to buying anything. If you’re in London then it’s definitely worth getting yourself down to London Modular who have a great range of stock and are very helpful lads, too. They stock most everything:

Rubadub are based in Glasgow but have a good online site and stock lots of stuff, too. They also stock the TipTop Audio Happy Ending Kits. Digital Village have also entered into the Eurorack world.

Elsewhere in the UK and Europe is Post Modular (annoying flash website!) and SchneidersLaden, both of whom are efficient and well-stocked. Always worth keeping an eye on eBay, too: lots of bargains to be had.

Finally, if you’re in the US ModWiggler now have a dedicated store as well as Control, Analogue Haven and Perfect Circuit Audio. Lots of manufacturers will let you purchase directly from them, too.

Conclusion

If you got to the end of this and you still don’t understand, or you would prefer to sit back and have someone far cleverer than me explain it, you can check out this excellent set of videos by The Tuesday Night Machines where he’s explained nearly everything you need to know in handy YouTube clips. Check them out:

Also, this sticky of ModWiggler is an absolute no-brainer for anyone starting out and the lovely guys at Synthopia have chipped in with their two cents on Eurorack companies.

In the coming weeks and months I’ll be adding new modular guides on the basic operation and patching of some of the above modules, how to clock your Eurorack with Ableton/Logic, how to get into audio processing and whatever tickles my fancy. Enjoy and happy patching!

If you’ve gotten this far and want to read on, check the next instalment in this series, Modular 102: East Coast Synthesis in Eurorack.