Synth & engines
Synth mode is where you play and design sounds. A sound is shaped across three pages — ENGINE, ENV, and FX — with an LFO strip above the tabs.
ENGINE — pick your sound
The engine picker sits at the top-right of the display. Each engine is a different way of making sound, with its own animated scene and its own four knobs:
| Engine | Character | Knobs |
|---|---|---|
| CLUSTER | shimmering stacks of detuned tones — pads and swells | SPREAD · DETUNE · COUNT · TONE |
| DIGITAL | wavetable scanning with fold and drive — digital grit | MORPH · SKEW · RING · DRIVE |
| FM | bright, punchy, bell-like FM | RATIO · BRIGHT · FEEDBACK · MOTION |
| PULSE | fat, analog-style pulse and saw through a filter | PWM · CUTOFF · RES · SUB |
| STRING | plucked physical strings | PLUCK · DAMP · POSITION · DECAY |
| PHASE | phase-distortion — glassy to gnarly | SHIFT · CURVE · PARTIALS · TILT |
| DNA | dual-oscillator hybrid with cross-mod — drones and growl | SHAPE · CRUSH · DETUNE · TONE |
| SAMPLER | plays your own samples across the keys | START · END · LOOP · PITCH |
| DRUM | sample-kit drum machine — see Drums | PITCH · IN · OUT · GAIN |
| WIDE | big stereo unison | SHAPE · CUTOFF · RES · WIDTH |
| THUMP | dual-oscillator bass and drum synth | TUNE · WAVE · PUNCH · DRIVE |
| CLOUD | granular clouds and textures | POSITION · SIZE · DENSITY · VARIANCE |
| TALK | a 16-band vocoder — shape sound with your voice, live | CARRIER · FORMANT · ATTACK · SIBILANCE |
| NINE | a synthesized analog-style drum machine — see Drums | TUNE · DECAY · TONE · SNAP |
FM, CLUSTER and PULSE are included free; the rest unlock with Spool Pro.
Previewing a locked engine
Locked engines aren’t hidden. Open one and you’ll see “PRO preview — silent”: the scene animates and all four knobs respond, so you can explore how it feels — it just doesn’t make sound. Playing a key brings up the unlock screen.
ENV — shape each note
The ENV page shows the envelope as a curve you can drag directly — attack, decay, sustain and release. Short attack and decay make a pluck; slow attack and a long release make a pad.
The same page sets the play mode:
- POLY — chords; every key gets its own voice.
- MONO — one note at a time (last note wins), envelope restarts on each note.
- LEGATO — mono, but slurred notes don’t restart the envelope.
- GLIDE — the portamento slider: slide smoothly in pitch from note to note. Its label lights amber when it’s active.
FX — one effect per track
The FX page holds the insert effect. Effects belong to tape tracks, not to sounds — each of the four tracks keeps its own effect, so switching favorites never yanks your reverb away. Pick from the 11-effect rack (see Mixer & effects for the full table).
LFO — add movement
The LFO strip (above the page tabs) opens spool.’s modulator:
- Five shapes — sine, triangle, saw, square, random.
- Rate — free-running, or beat-synced to musical divisions (1/16 up to bars).
- Depth, and a destination: any of the four knobs on the current page — engine or FX.
When the LFO is moving a knob, the knob’s arc animates in real time with a small tick marking your base value.
Next: Drums →