Lunar 24

An open-source desktop software musical instrument: an independent, unaffiliated study
of the ELTA Music Solar 42N — the analogue microtonal ambient drone machine and
semi-modular stand-alone synthesizer. Lunar 24 is not affiliated with, endorsed by, or a
product of ELTA Music / Analogue Solutions; it is a clean-room engineering study built from
the freely published manual and the project’s own fact mapping.

Lunar 24 aims to reproduce the Solar 42N panel layout and operating behaviour as
documented, and remaps its visual aesthetic through a restrained “moon” theme. The product
boundary is strict: it does not add sound sources, modulators, general-purpose routing
matrices, macros, plugin/DAW hosts, or a multi-preset library beyond the hardware’s own four
keyboard presets. The goal is architectural and behavioural, not a claim of calibrated or
identical sonic fidelity — that would require the hardware as a reference and would
over-claim beyond the evidence discipline in design/07-core-contract.md. Public audio may
inform perceptual tuning only; it is never presented as strict calibration.

This repository tracks its own source and design documents only. The ELTA Solar 42N
reference manual, panel render and effector catalog images are copyrighted third-party
material and are intentionally not committed — see design/reference/SOURCES.md for
their source URLs and checksums.

License

Apache-2.0. See LICENSE. Lunar 24’s own code is Apache-2.0; third-party
dependencies keep their own licenses (inventory: third_party/licenses/).

Target platforms

• macOS and Windows (standalone desktop app). No iPad/iOS/Android, and no Linux
  desktop product support (Linux may only supplement core CI builds).

Tech stack

• C++17 w/ warnings-as-errors, CMake.
• Standalone only; audio device + MIDI via a pinned iPlug2 submodule (P1); iPlug2’s
  IGraphics provides the UI. No AU/VST/CLAP/AAX/WAM, no WebView.
• The synth core is a framework-free pure C++ library — it never includes iPlug2,
  IGraphics, CoreAudio/WASAPI, window, or filesystem types. See design/07-core-contract.md.

Project layout

core/        framework-free synth core (public contract headers + implementation)
app/         standalone app / device / MIDI / UI adapter  (P1)
spec/machine/  canonical machine registry source of truth (JSON)
generated/   committed C++ headers generated from spec/machine/ (regenerate via tools/)
tools/       stdlib-only gates (generate_registry.py, check_core_headers.py, check_registry_negative.py)
tests/core/  framework-free unit + validation + regression tests
design/      design specifications and reference index
third_party/ dependency license inventory

Build

cmake -S . -B build -DCMAKE_BUILD_TYPE=Release
cmake --build build
ctest --test-dir build --output-on-failure

Governance

Design/engineering direction is set in the design docs. Development flows through feature
branches and PRs; commits follow Conventional Commits and each commit is a buildable,
testable logical unit.

Status

P0 is closed out and P1/P2 have exited MET; the work in flight is the GH#19 anti-aliasing
slices. P0 established the canonical machine registry, the framework-free core contract,
DeviceStateV1, a field-evidence policy, and the gates that keep them consistent and
switch-clean. This is a reviewed basis to build on, not a frozen/locked final
implementation; the concrete P0–P8 plan is in design/06-master-plan.md, and the live
reconnection point is design/00-status.md.