Guide 4 of 9 · Every Try it box opens the synth with its steps pinned on the rack

Modulation: making sounds move

So far every knob has stayed where you left it, unless an envelope was pushing it around. But a sound that never changes gets boring fast. Real sounds move all the time: a singer's vibrato, wind gusting, a wah pedal opening and closing.

Modulation means using one signal to change another over time. It's the reason modular synths exist: every knob with a jack next to it can be moved by any signal you patch into it. Once that clicks, you stop thinking "what does this module do?" and start thinking "what could move this?".

Source, destination, amount

Every modulation has three parts:

A source: something that moves. An LFO, an envelope, a sequencer, your hand on a pad.
A destination: the knob it moves. Filter cutoff, pitch, volume, delay time…
An amount: how far it moves it.

Change any one of the three and you get a different effect from the same patch.

The LFO: a hand that never gets tired

An LFO (low-frequency oscillator) is an oscillator that's too slow to hear, anywhere from one cycle every few seconds to a few cycles a second. You don't listen to it; you patch it into something and it moves that thing back and forth for you.

Rate sets how fast it moves.
Depth sets how big the movement is.
The wave buttons set how it moves: SIN sweeps smoothly, TRI goes up and down in straight lines, SAW ramps then snaps back, SQR jumps between two settings.

Kables draws a ring around any knob that's being modulated, showing where the signal is pushing it right now. Watch the rings: they're the best way to see modulation.

Try itLet an LFO turn the knob

The modules are on the rack with no cables. The VCA's Bias is already up, so this voice drones rather than playing notes, leaving you free to listen to the filter.

Patch the VCO's OUT into the filter's IN, the filter's OUT into the VCA's IN, and the VCA's OUT into the Output's MONO. A steady drone.
Patch the Keyboard's V/OCT into the VCO's V/OCT, so the keys change the pitch.
Now the modulation: patch the LFO's ± output into the filter's CV. The filter starts sweeping all by itself. Watch the ring around its Cutoff follow the LFO.
Change the LFO's wave to SQR: now the filter jumps between two settings.
Move the LFO's cable from the filter's CV to the VCO's FM jack and raise the VCO's FM Amt a little. Still on SQR, the pitch jumps between two notes: a trill.
Switch the LFO back to SIN and turn its Rate up to about 5 Hz: now the pitch wavers smoothly. That's vibrato. Same source, new destination, a completely different effect.

⏻ Build lesson 04 in KablesThe modules are waiting, unpatched. These steps come with you.

How much? Depth times amount

Two knobs set how far a modulation reaches: the source's own level (the LFO's Depth) and the destination's amount knob (the filter's CV Amt). If a modulation is too wild or too subtle, either one will fix it. Destinations without an amount knob take the signal as it is, which is where the next module comes in.

Up and down, or just up?

The LFO has two outputs. ± swings both ways around zero, from −Depth to +Depth, so it pushes a knob up and down from where you set it. + stays positive, from 0 to +Depth, so it only pushes up. Use ± for vibrato that wobbles around the note, and + when you want, say, a filter that only ever opens from where it sits.

Scale & Offset: the signal adapter

Signals rarely arrive at exactly the size you need. Scale / Offset is the tiny module that fixes that, and it does it with one rule: output = input × Scale + Offset.

Scale below 1 makes a signal smaller. Negative Scale flips it upside down.
Offset shifts it up or down.
With nothing patched in, it just outputs the Offset: a fixed voltage you can send anywhere, like a knob on a cable.

Try itToo much wobble

The LFO patch from the start of this guide, droning away, with a spare Scale / Offset beside the Keyboard.

Move the LFO's cable from the Filter's CV to the VCO's V/OCT. The pitch swoops a whole octave up and down: V/OCT has no amount knob, so the LFO arrives at full size. Far too much.
Put the Scale / Offset in between: the LFO's ± into its IN, and its OUT into the VCO's V/OCT, in place of the LFO's cable. It still swoops, because Scale 1 changes nothing.
Turn its Scale down to about 0.02: the swoop shrinks to a gentle wobble.
Turn the LFO's Rate up to about 5 Hz: vibrato.
Now turn the Scale / Offset's Offset up to 1: the whole thing jumps up an octave. Offset adds the same amount all the time, so it moves the wobble without changing its size.

⏻ Open it in KablesThese steps come with you, pinned on the rack.

Try itTwo more tricks

Two more jobs for the same little module: a second voice that always plays in harmony with you, and notes that get darker instead of brighter.

Play a few notes on A–K. Each key plays two notes at once, a fifth apart.
That's the Scale / Offset beside the Keyboard. Nothing is in its IN, so it sends out just its Offset, 0.58 (about 7/12 of an octave), into the second VCO's V/OCT, where it adds to the keyboard's pitch. Turn its Offset to about 0.33: now the second note is a major third above.
The other Scale / Offset sits between the ADSR and the Filter's CV. With Scale −1 and Offset +1 it turns the envelope upside down, so each note starts dark and brightens as it fades. Set its Scale to +1 and Offset to 0, and play: it now passes the envelope through unchanged, and notes start bright and darken, the usual way round.
Set them back to Scale −1 and Offset +1 and play again. Watch the ring around the Filter's Cutoff dip on each note instead of jumping up.

⏻ Open lesson 24 in KablesThese steps come with you, pinned on the rack.

Mixing modulation

A Mixer doesn't care whether it's mixing sounds or control signals. Mix a slow LFO with a faster one and you get a wobble that's more complex and less predictable than either. And because every input in Kables adds up all the cables plugged into it, you can also just patch two sources into the same jack.

Try itMix two LFOs

The LFO patch from the start of this guide, droning away, with its LFO moved down into a row: a second LFO and a Mixer wait next to it. Keep an eye on the ring around the Filter's Cutoff: it shows the mixed signal as it moves.

Route the LFO that's already moving the Filter through the Mixer: move its cable from the Filter's CV to the Mixer's IN 1, then patch the Mixer's OUT into the Filter's CV. Nothing changes yet: the ring still sweeps slowly.
Now the second LFO, next to it: turn its Rate up to about 6 Hz and patch its ± into the Mixer's IN 2. The ring now sweeps slowly and flutters fast on top, and you can hear both.
Turn the Mixer's level 2 down and back up: the flutter shrinks and grows on top of the sweep.
Turn level 1 all the way down: the slow sweep disappears and only the flutter is left.

⏻ Open it in KablesThese steps come with you, pinned on the rack.

You are a modulation source too

Modulation doesn't have to come from a machine. Controllers turn your movements into signals, and those signals can go anywhere an LFO could.

The XY Pad sends two signals at once, one for left-right and one for up-down, plus a gate while you touch it. Patch X to pitch and Y to a filter and you're playing two knobs with one finger.

The Gamepad and Phone Tilt modules do the same with a game controller's sticks and buttons, or by tilting and shaking a phone. They need the hardware to make any sound (lesson 41).

Where modulation goes next

Once you're used to LFOs, try sources that don't repeat: random voltages, chaos and physics. They get their own section in the melody & chance guide. And when modulation speeds up into the audio range, it stops sounding like movement and starts changing the tone itself: that's FM.

What to remember

Modulation is one signal moving another. Every modulation has a source, a destination and an amount.
An LFO is a slow oscillator you don't listen to. Rate is speed, Depth is size, the wave is the shape of the movement.
Same source, different destination, different effect: LFO on cutoff is a sweep, on pitch it's vibrato, on a VCA it's tremolo.
The rings around knobs show modulation as it happens.
Scale / Offset shrinks, flips and shifts signals so they fit.
Your hands, a pad, a gamepad or a phone are modulation sources too.