Modular synths and Eurorack: how modular synthesis works
A modular synth is built from separate modules, an oscillator, a filter, an envelope and more, that you connect with patch cables. Here is how a patch works, what control voltage and 1 V per octave mean, and what Eurorack is.
A modular synthesizer is built from separate modules, each with its own function: an oscillator makes a tone, a filter shapes it, an amplifier sets its level, an envelope shapes each note. You join the modules with patch cables, and the set of connections is called a patch. A semi-modular synth has a fixed set of circuits that you can still re-patch.
The modules
- VCO, voltage-controlled oscillator: makes the tone.
- VCF, voltage-controlled filter: shapes its brightness.
- VCA, voltage-controlled amplifier: sets its level.
- Envelope generator: a shape that rises and falls with each note.
- LFO: a slow wave that moves a setting up and down.
- Sequencer: steps through a series of values, such as the notes of a pattern.
Control voltage and 1 V per octave
Modules talk to each other with voltages. A control voltage sets a module's parameter: patch an LFO into a filter's cutoff input and the cutoff follows the LFO. Most modules use a pitch standard called 1 V per octave: each 1 V rise raises the pitch by one octave, so a sequencer or keyboard can play an oscillator in tune. Gates and triggers carry timing. A trigger is a short pulse that marks when something starts; a gate stays on for as long as the note lasts. In Eurorack they are typically pulses from 0 to 5 V.
A short history
The first prototype of the Moog synthesizer was shown at the Audio Engineering Society convention in 1964, and the first Buchla Modular Electronic Music System followed in 1965. After 1970 the market moved to semi-modular and all-in-one synths such as the Minimoog, and by the late 1970s modulars had fallen out of favor. A revival began in the late 1990s. Dieter Doepfer's smaller A-100 system led to the Eurorack standard, which other makers adopted from the mid 2000s.
What is Eurorack?
Doepfer specified the Eurorack format in 1995 and released the first Eurorack system, the A-100, in 1996. Modules are 3U tall, 128.5 mm, and their width is measured in HP, where 1 HP is 5.08 mm. They run on a plus and minus 12 V supply, with +5 V for some modules, and most use 1 V per octave for pitch. As of 2022, Eurorack had become a dominant hardware modular format, with over 15,000 modules from more than 600 makers. Larger 4U and 5U formats exist too.
Modular on a computer
Software modulars such as VCV Rack let you patch virtual modules with virtual cables on a computer, some of them modeled on historical modular systems. Many software synths also borrow the idea without cables: a modulation matrix lets you pick a source and a target from menus and set how far one moves the other.
Modular-style routing in Kiln
Kiln Synthesizer is not a modular synth, but its modulation matrix works like patching: route its envelopes, LFOs, Random, Chaos, macros, velocity, the mod wheel or MPE pressure and slide to targets such as each oscillator's pitch, level or wavetable position, or each filter's cutoff and resonance. The Kiln manual lists every source and target.
Questions
What does 1 V per octave mean?
The pitch standard most modules use: raising the control voltage by 1 V raises the pitch by one octave.
What is HP in Eurorack?
The unit of module width: 1 HP is 5.08 mm. Cases are described by their total width in HP, such as 104 HP.
Do I need hardware to learn modular synthesis?
No. Software modulars let you learn patching on a computer, and the same ideas, oscillators, filters, envelopes and control voltages, carry over to hardware.
