THE MODULARIUM — GUIDE

By Simon Fletcher

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✓ Full tutorial course (22 lessons + 4 challenges)
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What is a modular synth?

A modular synth is built from separate modules — oscillators, filters, amplifiers, envelopes — that do nothing on their own. You create sound by connecting them with cables. There is no fixed signal path; you decide how everything connects.

Jack types

Audio — sound signals CV — control voltage (pitch, filter, modulation) Gate — triggers (on/off pulses)

Click any two jacks (one output, one input) to create a cable — order doesn't matter. To remove a cable, click the small X near its input jack.

You can patch multiple cables to the same input. The signals get summed together — just like hardware modular. Try patching the sequencer pitch and an LFO to the same VCO V/OCT input for vibrato on top of melody.

Modules

VCO 1–4 — Oscillators that generate sound waves. Choose SAW, PULSE, SINE, or TRI. The FREQ knob sets base pitch, but is overridden when V/OCT is patched. PW controls pulse width (PULSE mode only).
NOISE — Noise generator with selectable COLOR (white, pink, brown). White is bright and hissy, pink is warmer and more natural, brown is deep rumble. Useful as an audio source or as a random signal to feed into Sample & Hold.
MIXER — Combines up to 3 audio inputs into one output with individual CH 1/2/3 level knobs and a master GAIN. Use this to layer and balance multiple oscillators.
VCF 1–2 — Two independent filters. CUTOFF sets where it cuts, RESO adds a peak. Two CV inputs: FREQ CV modulates cutoff (with FREQ AMT knob), RES CV modulates resonance (with RES AMT knob). Use in series (LP→HP for bandpass), parallel, or on separate sources.
VCA 1–2 — Volume gates. Silent by default (LEVEL=0). The CV input controls the level — patch an envelope here to shape the loudness of each note. LEVEL adds a constant gain on top of CV.
RING MOD — Ring modulator. Multiplies two audio signals together, producing sum and difference frequencies. Patch a sound source into SIGNAL and a second oscillator into MOD. Produces metallic, bell-like tones. DEPTH controls how much ring modulation is applied (0 = dry signal, 100% = full ring mod).
QUANTIZER — Snaps CV to musical notes. Patch between any CV source (Random S&H, LFO, sequencer) and a VCO V/OCT input. SCALE selects chromatic, major, minor, pentatonic, or blues. ROOT sets the key (C through B).
COMPRESSOR — Dynamics compressor. Reduces loud peaks and evens out volume. THRESH sets the level above which compression kicks in, RATIO controls how much it compresses, ATTACK/RELEASE set how fast it responds. Patch inline anywhere in the signal chain, typically before Master Out.
DELAY — Echo/delay effect. TIME sets delay length (up to 2s), FDBK controls how many repeats, WET/DRY mix the delayed and original signals. CV input modulates delay time for chorus/flange effects.
REVERB — Convolution reverb for placing sounds in a virtual space. SIZE sets the room length (small booth to cathedral), DECAY shapes the tail's drop-off, DAMP is a lowpass filter on the tail (dark/wooden vs bright/tiled), WET/DRY mix the reverbed and original signals. Chain it after DELAY for classic ambient washes.
ENV 1–2 — Two independent ADSR envelope generators. Each outputs a 0–1 CV signal when triggered by a gate. Use one for VCA (volume shape) and the other for VCF (filter sweep) or pitch.
LFO 1–2 — Two independent slow oscillators for modulation. Each outputs a repeating CV signal. Patch to a VCO's FM for vibrato, VCF FREQ CV for wah, VCF RES CV for drifting resonance, or PWM for pulse width animation. SYNC gate input resets the LFO phase to zero on each trigger for consistent modulation from note start. Use both at different rates for polyrhythmic modulation.
CLOCK — Independent trigger source. Fires gate pulses at a set BPM and division. Use it instead of (or alongside) the sequencer.
RANDOM S&H — Sample and Hold. On each trigger (internal clock or GATE input), it samples whatever is at its IN jack (or generates a random value if nothing is patched) and holds that value at the output. GATE OUT fires on every sample. Patch it to an envelope gate to sync note triggers with the random values.
CV/GATE SCOPE — Inline monitor for debugging. Patch CV or gate signals through it (IN→OUT pass-through for both CV and gate). Shows waveform, min/now/max values, and counts gate triggers. Use RESET to clear stats.
GLIDE — True audio-rate slew limiter (portamento). Patch between any pitch source and a VCO V/OCT for smooth slides. TIME knob is "seconds per octave" — bigger jumps take proportionally longer, just like hardware. Works on any CV signal: smooth an LFO into a lazy sweep, slew an envelope, smooth random S&H values, etc.
LOOPER — CV/Gate loop recorder, like a loop pedal for notes. Patch between a keyboard/sequencer and the synth voice. Records pitch and gate events in real time, then plays them back with optional looping. Includes a built-in metronome with adjustable BPM for recording in time. Pass-through while recording so you hear what you play.
KEYBOARD — Play notes from your computer keyboard (DAW-style layout). Lower octave: Z X C V B N M (white), S D G H J (black). Upper octave: Q W E R T Y U I (white), 2 3 5 6 7 (black). -/= shift octave down/up, hold Shift for +1 octave. Click keys with mouse/touch too. Also supports USB MIDI keyboards (plug in and play). 7 arp modes including ARP RUN (chord inversions). ARP LATCH holds notes after release for hands-free arpeggios. Outputs V/OCT CV and gate.
MIDI — Exposes MIDI controller signals as audio-rate CV outputs. BEND output sums into V/OCT for pitch bend (RANGE knob sets ±semitones). MOD output is the mod wheel (CC 1), AFT is channel aftertouch, EXP is the expression pedal (CC 11). All work like any other CV source — patch to VCF, VCA, delay, or anywhere.
SEQUENCER — 16-step sequencer. V/OCT output sends pitch CV (works with VCO, filter, or any CV input), GATE output triggers envelopes. Drag steps to set pitch, use the checkboxes below to enable/disable each step. The red ACCENT row fires the ACCENT gate output only on marked steps — patch it to a dedicated envelope gate to add TB-303-style emphasis (open the filter or boost volume on accented notes). CLOCK gate output fires on every step (use it to sync the drum machine or any external clock-in). 8 play modes including arpeggiator.
BASIC DRUMS — 10-track × 16-step drum machine with three synthesized kits (808, 909, FM). Voices: KIK, SNR, LTM, HTM, CHH, OHH, CLP, CYM, RIM, COW. Patch any gate source into CLOCK IN to advance the pattern one step per trigger (the sequencer's CLOCK output or the CLOCK module both work). RESET IN rewinds the step counter so you can set odd bar lengths from an arpeggiator. Audio OUT routes to the master or through any effect chain. PATTERN dropdown has 16 built-in kits including Four On The Floor, Boom Bap, Breakbeat, House, Electro, Techno, Latin, Reggae, Dembow and more. Free tier has the module with a preloaded sample pattern; pattern editing is Pro.
MASTER OUT — Final output to speakers with volume control and oscilloscope. LISSAJOUS button opens a fullscreen audio-reactive visualizer (ESC or double-click to close).

The basic signal chain

Most patches follow this pattern:

Sound source → Processing → Amplifier → Effects → Output

VCO OUT → VCF IN (oscillator into filter)

VCF OUT → VCA IN (filtered sound into amplifier)

VCA OUT → DELAY IN (shaped sound into delay)

DELAY OUT → MASTER IN (delayed sound to speakers)

SEQ GATE → ENV GATE (sequencer triggers envelope)

ENV OUT → VCA CV (envelope controls volume)

SEQ PITCH → VCO V/OCT (sequencer controls pitch)

Example patches

Acid Bass — Resonant filter sweep

The envelope controls both the VCA and the filter. Short decay + high resonance = squelchy 303 sound.

SEQ CV → VCO1 V/OCT

SEQ GATE → ENV GATE

ENV OUT → VCA1 CV

ENV OUT → VCF CV (envelope sweeps filter too!)

VCO1 OUT → VCF IN → VCA1 IN → MASTER IN

Try: VCF cutoff low (~300Hz), resonance high (~15), short decay, low sustain.

Add accent (pro): tick a couple of red accent checkboxes, patch SEQ ACCENT → ENV 2 GATE, and ENV 2 OUT → VCF CV alongside ENV 1. ENV 2 fires only on accent steps, pushing the filter open further — classic 303 accent.

PWM Pad — Animated pulse wave

The LFO slowly modulates the pulse width, giving the sound a rich, shifting character.

CLOCK GATE → ENV GATE

ENV OUT → VCA1 CV + VCF CV

LFO OUT → VCO2 PWM (LFO animates pulse width)

VCO2 OUT → VCF IN → VCA1 IN → MASTER IN

Set VCO2 to PULSE, LFO rate ~0.4Hz, depth ~0.4, PW ~0.3.

Sample & Hold — Random bleeps

Noise is sampled on each clock tick to generate random pitch CV.

NOISE OUT → RAND IN (signal to sample)

CLOCK GATE → RAND TRIG (clock triggers sampling)

CLOCK GATE → ENV GATE

RAND OUT → VCO FM (random pitch)

ENV OUT → VCA1 CV

VCO OUT → VCF IN → VCA1 IN → MASTER IN

Set RAND to external clock, range ~800.

Dual VCA — Envelope-controlled modulation depth

VCA2 controls how much LFO reaches the filter, so the wobble fades in with the note.

LFO OUT → VCA2 IN (LFO goes through VCA2)

ENV OUT → VCA2 CV (envelope controls LFO amount)

VCA2 OUT → VCF CV (shaped LFO modulates filter)

Without VCA2, the LFO is constant. With it, the modulation follows the envelope shape.

Tips

No sound? You need: a sound source (VCO/NOISE) → VCA with CV from envelope → MASTER. The VCA is silent without CV.
No notes playing? The envelope needs a gate trigger — from the sequencer or clock.
Knobs: Drag up/down to adjust. Hold Shift for fine control. Scroll wheel also works (Shift+scroll for ultra-fine). Double-click to reset.
Sequencer: Drag steps to set pitch. Use the yellow checkboxes to toggle each step's gate, and the red checkboxes below to flag an accent step. Patch SEQ ACCENT to a second envelope's gate to drive the VCF harder on accented notes — the 303 trick.
Arpeggiator: Set some steps to chord notes, mute the rest, select an ARP mode. The arp plays through the unique pitches of gated steps.
FM synthesis: Patch one VCO's output into another's FM input. Sine waves work best as modulators.
One output, many inputs: You can patch the same output to multiple inputs (e.g. envelope to both VCA and VCF).
Delay placement: Insert between VCA and MASTER for echo/reverb effects. Adjust WET for mix, FDBK for repeats. Patch LFO → DELAY CV for chorus/flange.
Debugging: Insert the CV/GATE SCOPE inline between any two modules to monitor signal levels or count gate triggers without breaking the signal chain.
Collapsing modules: Click the ▴ button in a module header to collapse it to a single line. Only unwired modules can be collapsed. Use COLLAPSE in the bottom bar to tidy up.