Throughout this Buyer's Guide, we'll talk about the different formats of modular synth, the cases and cables they utilize, and the many types of modules that help your custom rig create unique sounds. Read on to enter the wonderfully beautiful and strange world of modular synthesizers.
Modular Synth Formats
There are three main formats to consider when it comes to modular synthesis, and each has a different form factor. Since the 1990s, the Eurorack format developed by Doepfer in Germany has been adopted by lots of manufacturers, and is the most popular today.
Similar to the idea behind the 500 Series, the Eurorack is a standardized format that allows you to mix and match modules from various makers into a single case. Note that Eurorack measures sizes of width in "HP" (horizontal pitch), equal to 5.08 mm. The smallest modules are 2 HP wide, though this is barely bigger than a couple of cable jacks.
A total width of 84 HP is equivalent to a standard 19” rack, while 104 HP is a very popular width for standalone cases. The height is measured in "U" units, just like you’re used to, and Eurorack modules are 3U high.
Another format to consider is Moog/MOTM/Synthesizers.com (or just "dotcom") which are very similar to one another and are 5U high. Moog and dotcom modules come in widths that are multiples of the "Moog Unit" or MU, which is 2.125” wide, thus eight can fit in a standard width 19” rack. Similar to the Moog in size is the MOTM (Mother Of The Modulars), which is also 5U tall but comes in different module widths. All three of these types use a standard ¼” jack plug.
Running third in the popularity race is the Frac Rack (Fractional Rack) format, which is 3U high. Not as widely adopted as the other two, the Frac Rack has a strong DIY following. It can be used with Eurorack if certain mods are made, and both require 3.5mm jack plugs.
The three main formats are not all interchangeable, so you’ll need to decide which module format you desire and then commit to a case and cables made for that format.
Modular Synth Cases and Cables
Cases and cables are the least sexy (yet most important), parts of the system. Without them, you can’t achieve anything. In order to know which case you’ll need, you first have to decide what type of system you want to build, and how big it will be. A good rule of thumb is that you always buy a bigger case than you think you’ll need at first. Modular synthesis can make you more acquisitive than you expected, as you build your dream rig.
Most cases will come with a built-in power supply with the correct voltage for the modules, but it’s also important to know how much current your modules will need, so that you don’t exceed the power budget of a particular case. Vintage King Audio Consultants can help you plan this before you ever consider purchasing a module.
When it comes to cables, the choices are less complicated. For Eurorack and FracRack, the cable size is 3.5mm, also known as 1/8” TS. These are the same size as your mini headphone jack and are usually mono. The other size is our old friend the ¼” jack, used on the Moog format, which naturally increases the size of the patch points, and thus eats up more module real estate.
Specialty cables can be found to increase the flexibility of your routing beyond mono, single point-to-point patches. A "mult" cable act as a splitter to send the same signal to more than one point. Stackable cables also exist that allow you to plug one mono cable into the top of another, to piggyback on that patch point.
There is no rule as to how many cables you’ll need, but a good basis to start from is to get about two dozen for an 84 HP rig, with about half of those able to reach the full length of the case. You’ll want some smaller ones, so you don’t have lots of spaghetti connecting jacks that are right next to each other.
Once you’ve decided on a format, a case and the cables to go with it, you’re ready to go shopping for modules. This is where the sky is the limit. Once you have a few basic modules, you can get started synthesizing. Let’s look at the key modules next.
Type Of Modular Synth Modules
Modular Synth Oscillators
All modules either create or modify both audio and control voltage (CV) signals. Voltage is the root of all synthesis; with it, all things are possible. Without it, you have silence. Voltage can determine the pitch of a tone, or the cutoff frequency of a filter, and a lot more beyond that.
At the heart of any synthesizer is the oscillator, more technically known as the VCO or Voltage Controlled Oscillator. This is the unit that converts a voltage into an audible signal. Other units will modify this waveform in numerous ways, using their own voltages. You’ll need at minimum a single oscillator, and you’ll likely want a few more than that, to add variety to your rig. Modulars are usually monophonic, but extra oscillators can add different pitches to the signal, creating great depth.
Modular Synth Envelope Generators
Once you have a wave going, you want to ride it of course. Here’s where the Envelope Generator (EG) comes in. The EG is a dynamics module that creates control voltages that are used to shape four main parameters; Attack, Decay, Sustain and Release, or ADSR.
Amazingly, the manipulation of these parameters can take simple waveforms and turn them into a simulation of all kinds of sounds, from a pad to a kick drum. This is where you begin to "synthesize" a sound to create a synthetic version of what is normally an acoustic sound like a drum. There are numerous styles of EG available, and they are a key means of determining the capabilities and sound of your rig.
Modular Synth Voltage Controlled Filters
Along with the dynamics of a signal, you’ll want to control its equalization, and this is where the filter (or VCF) comes in. Once again, it’s voltage that does the trick, determining cutoff points for a Low-, High-, or Band-pass filter, along with Comb and Notch filters. The VCF is a very powerful way to shape sound (and very flexible), as any possible frequency is subject to your control.
Modular Synth Low Frequency Oscillators
As the name implies, low frequency oscillator module covers the lows. And by that we mean the very lows, as in below the human range of hearing. Why would you want to manipulate signals you can’t hear? Although the effect is not audible on its own, by interacting with audible signals the LFO can create vibrato, phasing, tremolo and more.
Suggested Modular Synth Low Frequency Oscillators: XAOC Devices Batumi, Intellijel Quadrax Quad Function/Burst Generator/LFO, Doepfer A-147-2 Eurorack Voltage Controlled LFO
Modular Synth Voltage Controlled Amplifier
The concept behind the VCA is simple. It uses voltage to control amplitude, thus determining the final signal before it leaves the synthesizer. But this module can be routed to different parts of the signal path to create other effects as well, such as modulation and triggers. The VCA is often controlled by the control voltage, making it program-dependent. And of course, other modules can be patched into it, such as an LFO to create tremolo by increasing/decreasing the volume at a specific rate.
Miscellaneous Modular Synth Modules
The world of modular synthesizers is an extremely diverse one. Every single day, synth wizards are creating new modules that cross the boundaries of the categories we've laid out in this Buyer's Guide. Whether they be sequencers, percussive, reverbs, delays, audio repeaters, or anything else, these miscellaneous modules are what can take your rig to another universe.
Pre-Configured Modular Synthesizers
If you don't want to build out your own Eurorack case, modular synth makers have made picking up a pre-configured set-up extremely easy. Make Noise has several different options like the standalone 0-Coast. Moog's Mother-32 semi-modular synthesizer is an extremely popular option for newcomers to modular and for the more advanced, the brand is also recreating some of their classic designs, including the IIIP.
Modular Synth Controllers
Synthesizers need some way of controlling the signal and triggering it on and off. The two typical ways are with a dedicated keyboard or a sequencer. These usually control a Gate switch, which is a simple On/Off trigger that sends a voltage to fire up another module like the Envelope Generator. Whenever a key on a keyboard is pressed, it engages both a pitch control and a gate, to tell the next module that the key for that pitch is engaged.
If you want to use a MIDI keyboard to run your modular, you’ll need to get a MIDI-to-CV module so that you can convert your MIDI signal into a Control Voltage. Of course, you don’t need a keyboard to run your synth; you can use a sequencer instead, creating a series of control voltages to create melodies from various oscillators. But having both keyboard and sequencer is the ideal option as they can work wonders together.
Creating Patches On Your Modular Synth
Once you have your modules in a powered case, you can start patching by using your cables to determine the signal flow or "patch." There is no right or wrong way to run a patch, though some are much more musical than others. It all depends on what you’re trying to create. The beauty of analog synthesis is that there truly are no borders. It’s a wide-open frontier whose horizon is determined only by your imagination.
In order to explore this frontier, do your research; listen to examples, check out a forum, and hear what others have done. The modular concept is infinitely expandable, and if you're a beginner, it’s best to follow a simple rule; Dream Big - Start Small - Leave Room to Grow.