Modular is not a fifth way of making a sound. It is the other four with the front panel taken off: every oscillator, filter, envelope and amplifier is its own box, and you decide with a cable what goes where. A fixed synth is one patch someone chose for you. A modular is every patch you have not made yet.
Where it began
In 1964 Bob Moog, working with the composer Herbert Deutsch, built his first voltage-controlled modules and showed them at the Audio Engineering Society convention in New York; the choreographer Alwin Nikolais was the first customer. In 1967 the company sold standardised systems and used the word "synthesizer" for them for the first time. Wendy Carlos's Switched-On Bach of 1968 sent modular sales up, and Moog kept making the System 35 and 55 until 1981. Early systems were large and expensive and went mostly to universities and a few wealthy musicians, which is why the Minimoog of 1970 put the common patch in one box.
Cables carry three kinds of signal
A patch is the arrangement of cables; it is the sound. Through those cables run three things.
| Signal | What it is | Example |
|---|---|---|
| Audio | The sound itself, about 10 volts peak to peak | VCO → VCF |
| Control voltage (CV) | A voltage that sets a parameter: pitch, cutoff, level | Keyboard → VCO |
| Gate, trigger, clock | A voltage that is either on or off | Key held → EG |
The rule that made it all fit together is one volt per octave: raise the control voltage by one volt and the oscillator goes up an octave. Moog developed it, and Doepfer and most makers since keep it, so a keyboard, a sequencer or a module from another maker tunes the same oscillator the same way. A gate is a voltage that stays high while a key is held; a trigger is a short pulse at the moment it is pressed; a clock is a trigger that repeats. On Doepfer's system anything above about 1 volt counts as on, 5 volts is typical, and modules tolerate up to 12.
| Does | Module |
|---|---|
| Oscillator; pitch follows CV at one volt per octave | VCO |
| Filter; cutoff follows CV | VCF |
| Amplifier; level follows CV | VCA |
| Envelope generator; a gate in, a rising and falling voltage out | EG |
| A slow oscillator used as CV | LFO |
| A row of voltages stepped through by a clock, with a gate at each step | Sequencer |
| Sample and hold; takes the input voltage at each trigger and holds it: random melodies from noise | S&H |
Eurorack
The format most modules come in today was specified by Doepfer Musikelektronik in 1995; the first A-100 system followed in 1996. Dieter Doepfer had built an Elektor Formant in the late 1970s and believed a smaller, cheaper modular still had a point. His numbers became the standard: front panels 128.5 mm high (3U, rounded for the rails), widths in HP where 1 HP is 5.08 mm, a plus and minus 12-volt supply on a ribbon cable, and 3.5 mm jacks for every signal. Doepfer alone listed more than 125 modules in 2016; by 2022 the format counted more than 15,000 modules from more than 600 makers. Mutable Instruments' open documentation shows the format in miniature: Plaits draws 50 mA from the +12 V rail and 5 mA from the −12 V, and its V/Oct input spans ten octaves; Clouds, the granular module of lesson 4, is 18 HP wide.
Why anyone bothers
A modular costs more, takes longer and forgets its sound when you pull the cables. What you get is a connection no fixed synth offers: an envelope into pitch, a sequencer into a filter, audio into a control input. Doepfer's own manual says a modular is an open system, that each sound has to be puzzled out and may never be exactly repeated, and that anyone who wants to hear all its sounds at the press of a button will be very disappointed. That is the point.
Sources
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