spiral

don't look down

20 HP

Hold a note and give it a clock. SPIRAL winds two arpeggios round it in contrary motion, one climbing as the other falls, both home on the centre every turn. ZOOM pulls everything round the note away, or rushes it in; the note never moves.

The SPIRAL panel: black, in gold dots a stone spiral stair seen from straight above, its next turn of steps a ring round a spiral of bare circuit board under the name: a round centre and two arms wound round it, twelve segments each. The big ZOOM knob under the spiral, KIND under it with five dots round it, the FALL button at the foot; CENTRE and STEP at the top corners, TURN, WIND, DEPTH and SWAY down the sides, ZOOM's and FALL's jacks under the spiral, UP's two jacks down the left and DOWN's down the right, BELL and TOLL either side of KIND, APART and FALLING at the foot. spiral at the top, daylight noise at the bottom.

Turn a knob: drag it or tap either side of it, roll the wheel over it or use the arrow keys; a double click puts it back. KIND clicks from stop to stop the same way; FALL is a button: press it and the spiral falls, hold it and it stays down. The patches step on by themselves until you touch anything.

A slow dark groove, a new centre every two bars: UP a glass on the right, DOWN a string on the left, a pad on the centre and a bell each turn. Listen plays the patch from its top.

example patches

The turn, the two lines, the fall and every out and light here are SPIRAL's engine, the module's own code, running in your browser. The groove, the sequencer and the voices are a stand-in rack.

The spiral

Each turn the two lines leave the centre together, wind out through the chord, UP above and DOWN below, and wind back to meet on it. Under the name, the arm ending on the left lights the notes above the centre, the other those below.

CENTRE: the note it circles, to the semitone. Move it and the next note winds round the new one.
STEP: the clock, a step a rise. Unpatched, eight steps a second.
KIND, a five-way switch: the chord they wind through. Fully left major, then augmented, minor at noon, minor with a major seventh, and fully right the diminished seventh.

Zoom

ZOOM, the big knob: everything round the centre at once. Turned up, the lines reach further and slow down, to four times as wide and as slow; turned down, they close in and speed up, to a whirl round the centre at four notes a step. The centre never moves. Its jack: a CV, added to the knob.
DEPTH: how far the lines reach at noon, from a quarter of an octave each way to four octaves.
TURN: how fast it goes round against the clock, from a note every four steps to four a step.

How the lines wind

WIND: how the two lines move. At noon a mirror, DOWN falling exactly as UP climbs. Turned left, DOWN holds still while UP moves, then fully left they climb and fall together, a span apart. Turned right they cross, each sweeping from the bottom of the other's range to the top of its own, through the centre twice a turn.
SWAY: when the notes come in a turn. Even at noon; turned right the lines hang at their edges and rush through the centre, like a swing; turned left the reverse.

The fall

FALL, a lit button and its gate: the spiral loses its grip and tumbles down through the chord, faster and faster, four octaves in eight notes, still turning. It lies at the bottom while you hold it, then climbs back a chord step every second note, to exactly where it left.

What comes out

UP, DOWN: the two lines, each a pitch and a gate, every note a note of the chord over the centre.
BELL, TOLL: the centre's pitch, and a gate as each turn begins, when the lines leave it together.
APART: how far apart the two lines are, 1 V an octave: 0 V where they meet, wide open when ZOOM pulls away. On a filter, the sound opens as they part.
FALLING: a gate, high from the fall until it's climbed back.

Inside

One board sits 10 mm behind the panel with everything on its front: the jacks, the knobs, KIND, FALL, the 46 LEDs and the whole circuit, the USB-C in a notch in its left edge. Each segment of the spiral has its own cell in a black printed baffle, lit by one to three white LEDs along it, so a segment lights evenly and the turn beside it stays dark. An RP2350 winds the two lines three thousand times a second.

The SPIRAL panel pulling away: the spiral lit far out along both arms round its centre, its knobs, jacks, KIND and FALL on.

Drag it or use the arrow keys to turn it; click it to take it apart.

Specs

Format

Width: 20 HP
Depth: 20.8 mm behind the panel
+12 V: about 45 mA dark, 75 mA in use, 190 mA at the most, its lights at their cap (estimated)
−12 V: about 5 mA (estimated)
+5 V: not used
Controls: a big knob, 4 knobs, a five-way switch, a lit button

I/O

CENTRE: 1 V an octave, −6 to +6 V, to the nearest semitone (0 V is C4); a 24-bit converter, calibrated; safe to ±12 V
STEP: clock, high past about 0.9 V, 4 ms to 4 s a step; unpatched, eight steps a second; safe to ±12 V
ZOOM: CV, added to its knob, 5 V the whole way; safe to ±12 V
FALL: gate, high past about 0.9 V: a rise falls, held high it stays down
Pitches: UP, DOWN, BELL: 1 V an octave, −5 to +5 V (a note past that folds by octaves), 16-bit, calibrated
Gates: UP, DOWN, TOLL, FALLING: 0/5 V, each note's at least 1 ms
APART: CV, 0 to 8 V, 1 V an octave apart

Engine

Brain: RP2350, 3,000 steps a second, 32-bit float
Clock: each step cut in 24; the gates about 3 ms behind STEP
Light: 46 white LEDs in 25 windows, 100 frames a second
Power cycle: it wakes still, the turn at its start; only the calibration is kept