Getting started with Eurorack modular synthesizers

What is Eurorack? Getting started with modular synthesizers, a simple guide. The current popularity of analogue synthesizers and synths in general can’t be understated. With so many innovations and inventions arriving on the market all the time, it’s hard to keep up with everything that’s available. If you're even remotely bothered by synthesizers, you've probably come across this oddball term "Euro-rack" or "modu-lar" and if curiosity has struck, well......that's probably how you've ended up here! Amongst the piles of wires and flashing lights there is sense to be made in this modular world, and here I'll attempt to provide everything you need to know to get started in with Eurorack synthesis so you can be up and running in no time. A little history of modular synthesis. Synthesizers themselves have fairly scientific beginnings, with early synths being made by guys in lab coats and consisting of modules with dedicated functions interacting with each other to make sound. It took some time for the synth market to add a keyboard, do away with cables and turn them into musical instruments to make the synthesizers we’re now familiar with. Early innovators of the modular format included the likes of Moog, Buchla, Roland, ARP, Serge and EMS. Modular synthesizers went from being the norm, to being the tools of the very rich and famous or “sound scientists”. Most modular synthesizers were pre-built systems that offered no integration with other manufacturers formats, if you had a Moog system - then you’d struggle to get that to talk to your Roland System 100m for example. It wasn’t until the early 90’s that modular synthesizers came out from behind the capes of synth wizards and back into the forefront of sound design. The Eurorack standard was pioneering in the early 90’s by Dieter Doepfer….yes that Doepfer. It was a format that Dieter stuck to and eventually, many many more companies adopted the form factor and we now have the incredible selection available to us now. All eurorack modules adhere to same 3U height standard, but many vary in width (aka HP or horizontal pitch) they also vary in power consumption and of course functionality. The Eurorack market is a thriving, vibrant marketplace of unique designs being produced by all kinds of different companies with multiple bustling forums dedicated to the subject. This approach to synthesis was completely fresh. Instead of buying a pre-designated system, people could now build synthesizers with the modules of their choosing. They could make the decisions that ultimately lead to the creation of their dream synth. Eurorack is the definition of expressivity in the electronic music realm. You build the synth, you make the choices on what modules and functionality you want and no single system is ever the same as the next. How you operate your system would be totally different to how everyone else works. It is the most inspiring and individual sound design tool available on the market right now. So you’re looking to explore this world of modular synthesis, what do you need? What can you do to get started? In this article I plan to explain exactly what’s required to get up and running and hopefully get you on the road to creating the synth you’ve always dreamed of. So first things first, let’s get the real basics out of the way and then we can move onto the juicy details. I’ll assume that most of you reading this have some idea of what a synth is and how it works, but for those that don’t, here’s a really brief overview of the concept of synthesis. Normally when people talk about synthesizers, most picture a keyboard encrusted with knobs and controls, with most modern synthesizers being based around a subtractive synthesis concept. All classic subtractive synthesizers are based around and include four main elements;

• An Oscillator for sound generation.
• A Filter for sculpting the timbre.
• An envelope generator for creating dynamic variation.
• An LFO for modulating the sound.
• And an amplifier for controlling the amplitude of the synthesized sound.

Most synths include these elements or modules, but it’s very rare for a keyboard synthesizer to offer any options to re-wire or change the signal path, the sound is ultimately “fixed”. That’s where the modular form factor comes in. Oscillators, VCO’s and sound sources: There are many types of oscillator available, most offer simple analogue waveforms such as square, saw and triangle and normally offer a wide range frequency control and CV and Gate inputs. CV is the universal format used within modular to transmit control message (control voltages) around a modular synth, CV on an oscillator usually allows for precise pitch control, with most modules adhering to the 1 volt per octave standard introduced by Moog. Gate is used to tell the oscillator when to switch on or off and how long to hold a note for. Though many oscillators in the eurorack world are simple analogue oscillators, they all sound slightly different as they all use a different form of circuitry to generate tones, so your best bet is to search for something that gets you the tones or waves you’re after. The Doepfer A-110 is dubbed the basic VCO, but it’s far from basic! It’s an affordable monophonic multi-wave oscillator that’s a really good starting point. But if you’re after a more complex wave generator, then take a look at the Oscillation module from Studio Electronics; paired with a mixer you can blend the 6 waves together to achieve unique waveforms and new sounds. If you’re after a less analogue approach then you’re not short of options here either, the NW-1 form Waldorf provides a true wavetable oscillator and the exceptional modules from French manufacturer Mutable Instruments also offer a huge array of digital tones and unique textures. A blend of analogue VCO’s and digital oscillators is always a good bet; you can mix the two signals together to get some really interesting results. I should mention here that most digital synths are based around DSP sound generation and don’t quite fit into the subtractive context mentioned earlier, but more on that later. Filters, VCF’s and modulation: One of the things that instantly drew me into Eurorack was the ability to pair any sound source I wanted with the filter I wanted, so for example if wanted to use a complex digital source like Mutable Braids with the warm analogue filter from the Sequential Prophet….then I could! Happy days. The staggering array of different filters on offer is something to research and enjoy. Since most vintage synthesizers had their own filter characteristic, it’s only natural for those highly desirable filter circuits to find their way into the modular standard. For example: If you want an MS-20, get the Intellijel Korgasmatron II, if you want a Yamaha CS-80 get the Studio Electronics SE88, if you want the Sequential Prophet Filter, get the Dave Smith DSM01, if you want a Moog filter then buy the AJH Synth Minimod VCF…..I could go on for hours, there are a hell of a lot of filter options out there. If there is synth you like the sound of, it’s almost a given that a version of its filter circuit exists in a eurorack design somewhere, so go out and find it. Modulation and Sequencing: Probably the coolest thing about Eurorack is the huge array of different modulation tools on offer, you do of course have your run of the mill LFO’s with multi-wave outputs, frequency control and the other standard fair. But there is a massive selection of complex envelope generators, LFO’s, Triggers, switches and all kinds of other modulation sources for creating forever evolving moving sounds. LFO’s are pretty simple; a low frequency audio signal that generates CV at its output and is used to interact with other CV enabled modules. Common uses of an LFO include filter cut off modulation, pitch modulation, amplitude modulation but other more exotic uses can include FM when the LFO is run at audio rates. Since an LFO has a rise and fall time, it can also be used to clock other modules to create time based modulation. Envelopes again are fairly simple to understand. Most envelopes use the ADSR standard, which means they offer Attack, Decay, Sustain and Release values for the CV signal they produce, once an envelope is gated or initialised the ADSR stage takes place:

• Attack denotes how quickly the envelope produces the sound, a faster attack, the quicker the sound responds, the slow the attack, the more progressive the signal raises in volume.
• Decay decides how long the note is held for at the maximum attack level before the sustain stage kicks in.
• Sustain decides how long the note is maintained at its maximum level until the key is released.
• Release takes place when the key or gate is released, the longer the release the longer the sound sustains for and vice versa.

Envelopes can be used to modulate pretty much anything within the modular format, but most common uses include pitch, filter response and VCA response. The key thing to remember with and envelope is that they always need to be gated or switched on to take effect and produce CV. Gate in CV out. Sequencers are really where modular outstrips any other synthesis format, the only limit here is the amount of case space you have and what your wallet can handle. There are as many sequencers and there are VCO’s and as many options to gate them and produce sounds. Complex gate trigger sources such as the TipTop Circadian Rhythm produce gates for drum voices and whatever else you can gate with a strong emphasis on song creation; this type of module paired with a group of trigger based sequencers can easily provide enough building blocks to create full cohesive songs. In our demo system, we’ve paired the Circadian Rhythms with the Audio Damage ADM06 since they both provide preset storage and a wide array of sequencing abilities when paired together. Sequencers can range from linear 8,16,32 and 64 sequencers to more complicated and random Euclidian style sequencers with a strong emphasis on music theory. Companies like Make Noise, TipTop Audio, Arturia, Intellijel, Analogue Solutions, Korg and Pittsburgh Modular all make gate or pitch based sequencers and with a completely unique take on the concept. Nothing is standard when it comes to playing sounds, you could pair something pretty simple like the Oberkorn from Analogue Solutions with a trigger sequencer like the Noise Engineering Numeric Repetitor and come out with some really obscure sequences. Find something you like the workflow of and learn it. If you want something simple and effective, the SQ-1 from Korg or Beatstep from Arturia offer a really simple user interface with a decent amount of connectivity at a really good price. So, modular synths are mostly based around the key concepts of subtractive synthesis: Sound generation that is plumbed into a filter and other modules, morphed and then output. But it’s the diverse array of modulation capabilities, tonal variety and routing options and timing, trigger and the staggering array of other options that make modular such a cool place to design sounds and even perform with. Semi modular, modular, pre-built – decisions decisions: Companies like Doepfer, Make noise, Pittsburgh Modular and Studio Electronics offer pre built complete eurorack synthesizers, whilst companies like Dreadbox, Korg, Analogue Solutions, Blue Lantern, Moog, Roland and Arturia offer Semi-Modular synthesizers that feature a normalized signal path with the option to re-wire the built in signal path as you see fit. It’s not a bad choice to buy a pre built system or invest in a semi-modular synthesizer if you’re unsure if you want to get into modular, since these systems remove the need to pick modules, case and a PSU and provide a completely built system you can get stuck into right away. But if you’re set on building your own personalized custom system, then read on. Let’s get designing: So to get started, the first thing you need to do is decide what kind of synth you want to build, since the only limitation is your imagination, so do what do you want?

• A complex monosynth with a wide array of modulation and routing options?
• A performance focused sequencing system with immediacy and easy programming?
• A system designed for audio manipulation and sound design?
• A drum machine?
• An effects processor?

The list could go on, but these are some of the popular examples. The best thing to suggest at this stage is do your homework. Good old fashioned research is absolutely key to understanding the variety of modules available and what they are capable of doing, it’s the only way you’ll work out the system you want. The KMR website is a good source of information, since we’ve got almost every module available online with detailed descriptions to help you pick what’s best for your design. System examples to get things going: So if you’re set on building your own system then this example system is a good place to start out to get a functioning two VCO monosynth with enough patchability to keep you busy: An example setup could include 2 VCO’s, a VCF, Envelope Generator, LFO and a MIDI to CV converter to get your DAW or MIDI controller talking to your modular. This style of system is more than enough to get started with and should provide ample building blocks to build new synthesis tones. Get on the case: The basic components that make up a eurorack system are the case, the power supply, modules and the cables. Generally speaking the cables are 1/8” 3.5mm mono jack cables, nothing special about their design but bear in mind that you’ll need cables of varying lengths and colours if you want to stay organised. Once you have an idea of the modules you want to start with you should also have an idea of the case requirements, there are a healthy choice of options when it comes to cases: Companies like Lamond Designs offer a custom build service which means you can tailor your case to fit the modules you want in a case that’s built completely for you. TipTop audio also offer a system called the happy ending kit, which provides a 19” rack chassis that you can easily house in any compatible 3U rack case if you already own a spare one or have space in your case for example. DIY is also an option here, TipTop offer a product called Z-Rails, which are the mounting rails found in Eurorack cases. You option here is to build your own box and mount the rails into the case. DIY is a great option for those handy with a saw and a sander! If you’re more inclined to get a lower cost option, then your best bet is to look to Doepfer. Their line of cases spans basic wooden enclosures such as the LC6 to gig ready systems such as the P6 and P9. My suggestion is to always buy a bigger case than what you think you initially need, since the module marketplace is always growing there’s absolutely no doubt that something really unique and interesting will pop up and you won’t have the space. Always budget for more space, and if your OCD strikes when you see an empty slot, you can always fill it in with a blanking plate. Make sure the power supply that comes with your case or the PSU you’ve picked supplies ample power to your system otherwise it simply will not work. So let’s pretend you have your system idea, your modules picked and your case in sight. Now the fun part begins, you can assemble your system! Ensure that you’ve thought through the workflow of your system to ensure optimum operation, for example it’s quite normal to have the main output on the bottom left hand side to ensure easy connectivity to external equipment. It’s usually best to follow input left to output right. Make sure you’re happy with the layout. Installing Eurorack modules, a beginners guide on how not to blow yourself up: Now I cannot stress how important the next part is, installing the modules whilst incredibly fun is the most dangerous part of working with a modular. If you get this bit wrong you could not only damage your modules you could damage the power supply itself! Eurorack modules connect to the power supply board using a ribbon power cable, to make sure you get this absolutely right, always….and I mean always read the manual from the manufacturer to make sure you install the modules correctly. As I said before, all eurorack modules are the same height, vary in width but they drastically vary in power consumption and connectivity to said power. Most manufacturers adhere to the standard -12v red stripe philosophy, where the red stripe on the ribbon cable connects to the -12v section of your module and PSU, but some use different standards completely. Most manufacturers indicate where -12v is with either a “red stripe here” or an obvious “-12v” marker, for the most part you can take this for granted that this is where you should connect the red stripe, just make sure you also connect the red stripe to the -12v on the power supply too. This part can get tricky if you’re working with lots of modules in a tight space, but take your time installing the modules, screw them in nicely and connect the power properly, enjoy this stage, it might seem laborious but you’re so close to having your own customised synthesizer. So there you have it, modules picked, installed and powered. So patch in some cables and start experimenting! The only limit here is the amount of cables and your imagination. We’ll delve deeper into more advanced synthesis techniques and workflow tips as this series progresses, so be sure to subscribe to our newsletter for the latest techniques, tricks and product announcements. For more information about Eurorack synthesizers call us on 020 8445 2446 or e-mail us sales@kmraudio.com By Tom Lewis