What is a modular synth?
A modular synthesizer is a synth taken apart. Instead of one box with its sound engine wired up inside, you get separate modules. Each one does a single job, and nothing makes a sound until you connect them with patch cables.
That sounds like more work, and it is. It is also the best way to understand how any synthesizer works, because every connection you make is an idea about sound that you can hear straight away.
You don’t need hardware to learn this. Everything below works in the Kables synth, in your browser.
Signals: everything is a cable
In a modular synth, every cable carries a signal: a value that changes over time. Some signals are fast enough to hear: that’s audio. Others are slow and move knobs for you: that’s control, usually called CV (control voltage). Two special kinds of control signal say when things happen: a gate is high for as long as a key is held, and a trigger is a short pulse that just means “now”.
The surprising part is that they are all the same kind of thing. Any output can go into any input. An oscillator can move a filter. An envelope can be listened to. Much of what makes modular interesting comes from breaking the “rules” on purpose.
The four jobs a module can do
Almost every module fits into one of four roles.
1. Make a sound: sources
An oscillator (VCO) repeats a wave shape over and over, and you hear it as a pitched tone. Its waveform decides the tone colour: a sine is pure, a sawtooth is bright and buzzy, a square is hollow. Noise is a source too: hiss with every frequency at once, perfect for wind, surf and drums.
An oscillator never stops. Patch one straight into the Output and it drones forever, which is why the next two roles exist.
2. Shape the sound: filters and VCAs
A filter (VCF) removes part of the frequency range. A low-pass filter cuts the highs, so turning its cutoff down makes a sound darker. Turn up its resonance and it whistles at the cutoff. Starting from a bright waveform and filtering it is called subtractive synthesis, and it is how most classic synth sounds are made.
A VCA is a volume control that another signal can turn. With nothing on its control input it stays shut, so a VCA plus a control signal is what turns a drone into notes.
3. Move the knobs: modulators
This is where modular comes alive. An envelope is a shape that rises and falls each time a note is played: Attack, Decay, Sustain and Release (ADSR). Patch it into a VCA and notes fade in and out; into a filter and each note starts bright and closes down.
An LFO is an oscillator too slow to hear. Into pitch it gives vibrato, into a VCA tremolo, into a filter a slow sweep. A Sample & Hold grabs a random value on every clock tick, giving the classic “computer burble”.
Using one signal to change another is called modulation, and in a modular synth you decide what modulates what.
4. Decide when: clocks, sequencers and controllers
A keyboard sends two signals: a V/OCT pitch (which note) and a gate (whether a key is held). A clock sends steady triggers, and a sequencer steps through a pattern of notes on each one. Euclidean sequencers spread hits evenly over a bar and turn out surprisingly musical rhythms.
Your first patch, in words
The classic beginner patch is a single voice:
- Keyboard V/OCT → VCO V/OCT. The keyboard picks the note.
- VCO OUT → Filter IN → VCA IN → Output. The sound flows left to right.
- Keyboard GATE → ADSR GATE. Pressing a key starts the envelope.
- ADSR OUT → VCA CV. The envelope opens the VCA, so you hear a note only while the envelope is up.
Add ADSR → Filter CV and every note gets the brightness sweep that makes synths sound like synths. That’s the heart of the first three guides, and you can build it yourself in five minutes with the guided build.
Why learn on a modular?
Fixed synths hide the signal path behind a panel of knobs. A modular makes you build it, so you learn why a sound behaves the way it does. Once you know that an envelope opens a VCA and sweeps a filter, the front panel of any synth (hardware, plugin, or the one in your DAW) makes sense.
The names in Kables are the ones used in hardware Eurorack systems, so everything carries over if you ever buy a case.
Where to go next
- Read the guides, starting with oscillators. Each one hands you patches to play as you read.
- Look up a word in the glossary.
- Browse what each of the modules does, jack by jack.