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LACUNA + ORBITA — mesh-0.3: both instruments stereo

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@Eight4aWish Eight4aWish released this 05 Sep 14:20
· 19 commits to main since this release
mesh-0.3
f72e538

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. Both are stereo as of this release.

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, the membrane drawn live.

ORBITA — the same mesh run a thousand times slower, with circular paths
through it read at audio rate as wavetables. 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-0.2

ORBITA is stereo. Two scan circles, the right a quarter of the annulus
further out. Two radii rather than two points on one circle — points on a
single circle differ only by phase, which gives width but combs in mono, while
two radii are genuinely different wavetables. Measured L/R correlation runs 0.48
to −0.19 across the radius sweep and −0.03 on the drone.

It cost no multipliers: the scan is sequential and uses about thirty of the
1250 cycles in a sample, so the state machine walks the sample-and-blend
sequence twice with a channel bit selecting which radius enters the shared
multipliers. Both circles are drawn on the display — the left lifts green, the
right green and blue.

Expect ORBITA's right channel 3–5 dB below the left: it sits further out, where
the membrane moves less. That is physical rather than a scaling error.

Downloads

file for
lacuna-mesh-0.3-r5.tar.gz LACUNA, 1280×720p60 — capture cards, most monitors
orbita-mesh-0.3-r5.tar.gz ORBITA, 1280×720p60
lacuna7-mesh-0.3-r5.tar.gz LACUNA, 720×720p60 — Waveshare square panel
orbita7-mesh-0.3-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-0.3-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.
  • 19 of 28 multipliers used on ORBITA. Anything needing a genuinely
    parallel datapath, rather than another pass of the existing one, has nine.
  • 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.
  • Four days old and played by one person on one module.

Documentation: LACUNA ·
ORBITA ·
design note ·
provenance

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

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