fringe by daylight noise

fringe

it feels you walk in

20 HP

A wavefolder made of light. A real laser, split in two and bounced off two mirrors on piezo discs: your sound moves the mirrors, and what comes back is a cosine of how far they've gone. It's the most sensitive thing in your rack. LOCK holds it dead still, or lets the room play it.

The fold

The laser's split in two, each half bounces off a mirror, and they meet again. Where the paths match they add; move a mirror 165 nanometres and they cancel. Glue that mirror to a piezo disc, drive it with your sound, and your sound goes through a cosine. Small signal: clean. Bigger: it folds. It can't go past the light it has, so however hard you drive it, it gets no louder and nothing clips. A triangle comes out as a vowel, a saw as hard sync, a sine as FM.

FOLD: how far the mirrors go, from a kiss to a dozen folds.

BIAS: where in the cosine it sits. Three fringes across the whole turn, so a twelfth of the knob takes it from odd harmonics to even, and the fundamental goes.

A: the quick mirror. It rings at about 4 kHz and can't follow past that.

B: the heavy mirror, with a brass weight on it. It rings at about 700 Hz. It's for bass, a kick and anything slow, and what comes out is the cosine of the two mirrors' difference: B phase-modulates A, and the same low sound on both all but cancels.

CROSS: how much of A reaches B. Noon, none. Fully right the mirrors part and the folds double. Fully left they move together and cancel, except where the heavy one can't keep up: a filter made of mass.

The light

There are no LEDs on it. A beam splitter has two exits, and each window is one of them: the same rings in negative, because where one's bright the other's dark. The rings are the sound's own light: the dark spot at the middle is where the part you hear left for the photodiode. One ring born there is one whole fringe, two folds. Past what the eye can follow they fade, vanish, and come back the other way round as FOLD goes up. It's a Class 1 product, enclosed: the beam stays sealed in its block, and what reaches the glass is spread thin and ground.

LIGHT: how hard the laser runs. Coming down it stops being one clean colour, the fringes go grainy and at threshold they melt, the fold goes out of the sound and a hiss comes up. Under that it's dark.

LIGHT (the jack): your sound in the laser. It comes out of both exits together, with the fold across it in opposition: a ring modulator made of light. Sum the exits and you've got your sound back. Near threshold only its peaks lase, so it gates the fold.

The room

A warm hand near a window, a breath, somebody walking past, a kick coming up through the floor: all of it moves the mirrors or the air between them by a fraction of a wavelength, and the fold leans, even harmonics swapping with odd.

LOCK: fully left the room plays it. Noon, a servo takes out the slow drift and footsteps still get through. At full it doesn't move. It only has so much reach: past that it lets go and hops back a whole fringe. Its jack takes a gate or a CV.

Knock on it: the panel's the instrument's body. A tap rings both mirrors through the cosine, with anything or nothing patched: a low bong and a high tink. LOCK barely touches them: they're too quick for it.

Your hand: warmth is slow. Rest it there and the rings walk.

What comes out

BRIGHT, DARK: the two exits, a true anti-phase pair. On headphones it's strange and wide. Sum them and the fold's gone, every time, because the light's all still there.

FLOOR: the room, read by light: the rack's own shaking, read to a fraction of a nanometre, with the mirrors' drive taken off. A microphone for the case. Drive it hard with high notes and it can't keep count, so it holds.

DRIFT: the same reading, slow: the warmth, as a CV, 1 V a fringe.

SLIP: fires each time a whole fringe goes by, with LOCK off: a clock made of 329 nanometres, a burst when you hit the panel. With LOCK on, only when it lets go.

Specs

Format

Width: 20 HP
Controls: 5 knobs, a panel to knock on
Laser: enclosed, designed for Class 1, not yet tested

Inputs

A, B: audio, to the mirrors
LIGHT: audio or CV, to the laser
FOLD: CV, 1 V a tenth of the knob
BIAS: CV, 1 V half a fringe
LOCK: CV or gate, 0 to 5 V

Outputs

BRIGHT, DARK: audio, about ±5 V
FLOOR: audio, 0.2 V a nanometre
DRIFT: CV, ±5 V, 1 V a fringe
SLIP: trigger, 5 V