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LACUNA + ORBITA — mesh-0.2: stereo, and a smooth scan

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@Eight4aWish Eight4aWish released this 05 Sep 06:03
· 25 commits to main since this release
mesh-0.2
b5bc39e

This is not an apfaudio release. It is a personal fork of
apfaudio/tiliqua adding two bitstreams
of my own. Upstream's own releases (v1.0.2 … v1.2.1) are the ones to use
for stock Tiliqua firmware. Everything upstream here is unchanged.

Two instruments built on the same 32×32 finite-difference membrane, differing
entirely in how it is driven.

LACUNA — a struck membrane whose hole is the instrument. The boundary is a
comparator rather than an array, so the geometry can change every sample and
becomes a modulation destination rather than a setting. Eight geometries, exact
1 V/oct, and the membrane drawn live.

ORBITA — the same mesh run a thousand times slower, with a circular path
through it read at audio rate as a wavetable. Scanned synthesis in the
Verplank/Mathews/Shaw sense: pitch is the scan rate, so a held note morphs while
staying in tune. A concentric circle never crosses a concentric hole, so the
asymmetric geometries are the interesting ones — the slit gives one notch per
revolution and a full harmonic series, the square hole four notches.

What is new since mesh-0.1

LACUNA is stereo. Two pickups a quarter turn apart at the same radius. Real
decorrelation rather than a widener: measured L/R correlation is 0.50–0.60 on
the solid heads and −0.15 to 0.05 on the ring geometries, because angular modes
differ between the two positions while radially symmetric ones stay common — as
a struck drum does. A mirrored second pickup measures 1.00, which is mono with
extra steps, and +x would have been silent on the slit preset.

ORBITA samples between cells, not on them. The scan carries its position to
a sixteenth of a cell and blends the four cells around it. Waveform roughness
went from 0.579 to 0.029–0.094, and the radius control from 16 steps to 256.
This was the defect that made the previous release want reverb over it.

LACUNA's output saturates instead of wrapping. Accumulated strikes could
push past what a 16-bit output holds; it truncated, turning a loud moment into a
full-scale flip. An occasional click that only happened when playing hard.

Also: the strike and both pickups are drawn on the membrane, ORBITA's pitch
range covers eight octaves from 27.5 Hz, and its display shows the scan circle
unrolled as a waveform strip.

Downloads

file for
lacuna-mesh-0.2-r5.tar.gz LACUNA, 1280×720p60 — capture cards, most monitors
orbita-mesh-0.2-r5.tar.gz ORBITA, 1280×720p60
lacuna7-mesh-0.2-r5.tar.gz LACUNA, 720×720p60 — Waveshare square panel
orbita7-mesh-0.2-r5.tar.gz ORBITA, 720×720p60

Hardware R5 only. A cheap HDMI capture dongle will not lock to 720×720 — it is
not a standard timing, so use the 1280×720 builds with one.

pdm flash status                     # see what is in the eight slots
pdm flash archive lacuna-mesh-0.2-r5.tar.gz --slot 3

Limitations

  • ORBITA has no tension control. All four jacks are spoken for; λ² is a
    per-preset constant. The strike position exists in the mesh and ORBITA does
    not drive it, for the same reason.
  • ORBITA uses 19 of 28 multipliers, which is the resource that runs out
    first and what makes a stereo pair of scan circles a real cost.
  • LACUNA's geometry FM uses a hard mask, so a fast sweep of in3 is broadband
    noise at the boundary. An energy-conserving moving boundary is an open problem
    in the literature, not a coding task.
  • Three days old and played by one person on one module.

Documentation: LACUNA ·
ORBITA ·
design notes ·
provenance

Licence CERN-OHL-S-2.0, following upstream.

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