CV, Gate and Triggers
To harness the power of these semi-modular synths, you’ll need to become fluent in the languages these musical devices use to communicate. A standalone analogue synthesiser’s individual sections will be prewired under the hood: turn a knob to alter a particular voltage and change the resulting sound. The individual modules that make up a modular system, however, must be patched together with cables, in order to make those electrical connections manually. These analogue signals are known as control voltages, or CV.
Again, a semi-modular synth is the middleman between standalone synths and an all-out modular rig. On the face of it, one can act as a ‘regular’ standalone synth: all of its connections are ‘normalled’ by default, meaning that you can fire it up and make sounds immediately, no patching required. It’s the inclusion of a patchbay that sways the instrument towards the modular world. Grab a fistful of patch cables, make new connections in that patchbay, and you’ll break those default routings to make new ones internally. Or, to go further, shuttle those CV signals to and from a proper modular system, or even other semimodular synths.
Learn the language
Put simply, modules output control voltage pitch and/or gate data, and other modules can receive that data. Unlike the universal protocol of MIDI, which can trigger synths polyphonically and transmit multiple messages with ease, a single stream of control voltage data is monophonic. Plus, CV signals aren’t standardised from manufacturer to manufacturer. The more common implementation – invented by Bob Moog – is the linear standard of volts per octave (V/oct) whereby an increase in one volt results in a pitch jump of one octave; hertz per volt (Hz/V), meanwhile, as used by many older Korg and Yamaha synths, uses a method whereby a doubling in volts equals an increase in one octave. Without getting too bogged down in these technicalities, you need to know which CV standard each of your instruments sends and receives, to ensure they’re talking the same ‘language’.
Aside from ‘pitch’ CV, modular and semi-modular systems also use other types of voltages for general ‘go’ and ‘stop’ messages, known as gate and trigger signals. Imagine a keyboard sending out on/off data to an amplifier module: its voltage is at zero when no note is pressed, and its voltage jumps up to max level (say, 10v) when a note is pressed; let go of the key, and the voltage resets back to zero again. A trigger signal, meanwhile, is like the square-shaped gate signal, except it’s simply a short-duration spike in voltage. In the modular world, gate and trigger signals are used to trigger drum machines, restart clocks, reset sequencers and so on. As these are essentially just square-shaped voltages, any square wave signal can act as this basic ‘on/off’ message – for example, many electronic musicians send out a short, sharp rimshot sound from a drum machine to retrigger a synth’s sequencer and keep the two instruments in time.
Get creative
Once you’ve got your head around CV and how it works, you can begin exploring its vast possibilities. Let’s consider Arturia’s MiniBrute 2, a semimodular analogue monosynth with a 48-point patchbay. In its default state, the synth’s four-stage ADSR envelope governs filter modulation, the two-stage looping AD envelope affects amplitude, while LFOs 1 and 2 are hardwired to various sections – the blue text on a parameter indicates these default connections. However, by patching these modulators’ outputs into different inputs on the patchbay, you can quite easily replumb the normalled configurations and make fresh connections. Need more control over amplitude shape? No worries – rewire those two envelopes and use the ADSR to shape volume! Want to increase a parameter value as you play higher up the keyboard? Simple: patch the KBD output into said parameter’s input. This kind of rewiring can quite obviously open up more and more doors for creative sound design.
Rewiring can open up more and more doors for creative sound design