field: a 20 HP six-band resonant filter, by daylight noise

field

20 HP · filter

Six resonant bands, drawn as six rings of lit glass round the big knob. Patch a second sound into STRIKE and it puts up a wall against the first: clockwise it cuts its own shape out of IN, so a kick punches a hole in a pad exactly its shape; counter-clockwise, IN sounds only where it does. Turn RES up and the six bands ring on their own, a six-note chord. The rings ripple when it's struck.

Six bands

Six band-pass filters side by side, the innermost ring the lowest. With RES down they split IN into six bands and what's left between them, and put it all back together: the outs are IN, untouched, until something rings or strikes. Turn RES up and the bands narrow and lift into peaks at their six frequencies; past the top of its travel they ring on their own, a steady six-note chord, and FIELD is a voice.

FREQ: the big knob. All six bands together, the lowest from 30 Hz to 2 kHz across its travel.

V/OCT: a volt an octave on top of FREQ, −2 to +8 V. A self-oscillating chord follows it within a few cents (the engine, in its tests, within a fifth of a cent).

SPREAD and its CV: the bands' spacing. Fully down they sit inside a minor third, a cluster; around two thirds of the way they hold the harmonic series, 1 : 2 : 3 : 4 : 5 : 6, on a stretch of the knob that doesn't move; fully up they stretch to a struck bar's overtones, the top band nearly nineteen times the bottom.

RES: from no resonance, through peaks 26 dB over the bands, to the six bands ringing on their own. Each band's ringing is held at a level from inside: loud input compresses it rather than clipping it.

The wall

STRIKE has six bands of its own, at the same six frequencies. However loud STRIKE is in each one decides how much of IN gets through in the same place. CARVE says which way.

CARVE clockwise: where STRIKE is loud, IN is cut, up to 44 dB, band by band. A kick into STRIKE punches a hole in a pad in IN the kick's exact shape, its low bands as its pitch falls; a voice cuts its vowels out of a wash of noise. Bands two or more away from a struck one move less than 3 dB.

CARVE counter-clockwise: the reverse. IN sounds only where STRIKE does, each band following STRIKE's: close to a vocoder. With nothing in STRIKE, nothing comes out.

CARVE at noon: STRIKE does nothing. Its CV adds a fifth of the way a volt, either way.

MEND: how fast the field closes again after a strike, from 10 ms (a gate) to 2 s (a slow swell back). A strike opens it in about a millisecond, once its band has heard it.

STRIKE unpatched: it's normalled to IN, so IN strikes itself. Clockwise, the loud bands push themselves down, a spectral leveller; counter-clockwise, only the loudest bands sound.

Outs

OUT L and OUT R: the first, third and fifth bands left, the second, fourth and sixth right, and what's between them on both. While OUT R is unpatched it's summed into OUT L, so OUT L alone is the whole field.

STRUCK: how hard the field is being struck, as a voltage: STRIKE's six bands together, 0 to 8 V, 6 dB a volt, falling at MEND's rate. Patch it anywhere a kick's shape is wanted.

The panel

The six rings are the panel itself: hexagons of bare fibreglass, no copper and no mask, every knob and jack mounted through them, each ring broken round each part and each label so the labels read on black, lit or not. That leaves 27 pieces of glass, each over its own channel of a black printed baffle with its own LEDs, 54 in all. Each ring glows with its band's level; a strike sends a ripple out from the innermost to the outermost in about 120 ms, and the rings it cut stay dark until MEND lets them back.

Above the field, the fingers of two hands pressed flat against the glass from the other side, in exposed gold, from a photograph. Their palms are printed on the back of the panel, black over copper: in room light they can't be seen at all, and when the rings light up they're a shadow in the glow.

Specs

Format

Width: 20 HP
+12 V: about 120 mA, 200 mA with the field fully lit (the design's estimate)
−12 V: about 10 mA
+5 V: not used; 10-pin header
Panel: 1.6 mm FR4: bare glass rings, ENIG gold through black mask
Controls: 5 knobs, no switches

I/O

IN: audio, ±5 V with room to ±9; 100 k
STRIKE: audio, the same; normalled to IN
V/OCT: all six bands, 1 V an octave, −2 to +8 V
CV: SPREAD's and CARVE's, ±5 V
Outs: OUT L, OUT R: ±5 V into 1 k; OUT R summed into OUT L while unpatched
STRUCK: 0 to 8 V, 1 k

Engine

Brain: RP2350, 46.875 kHz, 32-bit float
Converters: PCM1808 in, PCM5102A out, on one I2S clock
Bands: six on IN, six on STRIKE
Light: 54 RGB LEDs behind 27 pieces of glass, their current capped
Firmware: over USB-C or the debug header, on the back