tonewheel91

A standalone, component-modeled electromechanical tonewheel-organ instrument in pure C23. Ninety-one always-running tonewheels behind a gear-ratio table, a key-contact/busbar network with taper, loudness robbing and key click, percussion, a vibrato/chorus scanner, stateful preamp drive, and a two-rotor rotary speaker. Live-first: the primary driver is a Linux ALSA MIDI-in / PCM-out loop; an offline Standard MIDI File renderer is the deterministic test twin.

Status: M7 landed — wear, the structured deviations: per-wheel level spread, tooth-profile harmonics, motion AM at each wheel's own rotation rate, an asymmetric pickup nonlinearity, leakage structured by the generator's bin/shaft layout (not the musical order), and a 60 Hz mains line, all behind one wear knob. wear = 0 is the idealized reference and reproduces every pre-M7 render bit-for-bit — asserted against pinned pre-M7 signatures in test.c and the recorded exhibit hashes; the shipped default is 0.2 (tolerance effects exist on a factory-new unit), so an idle organ now carries its ~-44 dB noise floor. Every depth except the pickup's measured alpha is a [FOLK]/[decision] working value (docs/constants.md secs 11.1/12.1/13.1) — the by-ear pass against reference recordings owns them. Evidence: docs/m7-evidence.md back through docs/m1-evidence.md. Post-M7 warmth pass: the preamp drive kernel is now derived from a circuit-true triode reference (docs/warmth-evidence.md; the rotary's 40 W ceiling keeps the M5 odd kernel) — make warmth scores the stage against the reference, ./build/exhibit_warmth render bakes A/B wavs of the old vs derived voice. Post-M7 depth pass: a key's nine contacts are now addressable by how far the key is held down, not only by how fast it was struck (docs/depth-evidence.md) — poly key pressure carries the travel, nine make points with a break-below-make band, and the section 6.1 merge law folds the partial contact set with no new DSP. Depth also corrected the percussion trigger, which now follows the 1' contact — the sensing line the sources always described — instead of the note event, with the 34 ms re-arm RC modeled so the sensing line's own bounce cannot retrigger it. A half-press therefore fires no percussion, and a held key's travel can fire it with no note event at all. That moved the percussion-on baselines and nothing else: every percussion-off signature, the M7 wear identity anchor included, reproduces bit-for-bit.

A second instrument shares the repo and the kernels: ep73, a tine electric piano (docs/piano-backlog.md). It is a sibling core, not a framework — 73 struck voices of three clamped-free tine modes each, a per-voice asymmetric pickup, and velocity that scales loudness and timbre for the first time in this codebase. EP0 pins its constants (docs/ep-constants.md), EP1 lands the voice bank offline (docs/ep1-evidence.md), and EP2 adds dampers, the sustain pedal, panic, the live ep73 binary and an instrument switch on render_midi (docs/ep2-evidence.md). Later passes add the pinned hammer voicing, tremolo, shared drive stage, cabinet and per-note condition model. No organ core translation unit depends on the EP core, the instrument switch defaults to the organ, and the organ's pinned signatures — the whole-song render hashes included — reproduce bit-for-bit.

make test      # core, hosted-boundary and MIDI-dispatch checks
make exhibit   # renders the evidence WAVs into build/
make viz       # renders the evidence PNGs into docs/viz/
make           # also builds the live driver

./build/tw91 -d hw:CARD=AG06AG03 -e 4      # demo chord on the rig
./build/tw91 -d hw:CARD=AG06AG03 -m hw:X,Y,Z   # live: amidi -l
               # poly key pressure (0xA0) = per-note key depth:
               #   how far the key is held, 0..127 over the travel,
               #   deciding how many of its nine contacts are made
               # CC11 swell, CC70..78 drawbars, CC120/123 panic,
               # CC80..83 percussion (on/off, 2nd/3rd, fast/slow, soft/normal)
               # CC84 vibrato/chorus (value/19: off, V1..V3, C1..C3)
               # CC85 drive (value/127)
               # CC86 rotary mode (value/32: bypass, chorale, tremolo, brake)
               # CC87 rotary speed switch (chorale/tremolo), CC88 balance,
               # CC89 width, CC90 rotary drive
               # -r rate -p period -n periods -g gain
               # -2 two-manual touch-surface protocol: notes and key
               #    depth on ch1+ch2 merge onto the one manual; CCs are
               #    honored on ch1 only

./build/ep73 -d hw:CARD=AG06AG03 -e 4       # the electric piano
               # notes 28..100, velocity -> loudness and timbre
               # CC64 sustain pedal, CC120/123 panic
               # CC85 drive, CC91 tremolo, CC92 cabinet, CC93 condition
./build/render_midi -I ep73 ...             # its offline twin

Layout

src/     freestanding core (no OS, no libm, no allocation): generator,
         contacts, percussion, vibrato/chorus scanner, preamp drive,
         rotary speaker, MIDI byte parser; and the ep73 struck-voice
         bank, which includes the organ's header for the shared kernels
         and is included by nothing in the organ
driver/  hosted layer: WAV and PNG writers, offline exhibits, and
         render_midi (SMF in -> stereo WAV out, the live driver's
         deterministic twin for whole songs; renders logged in
         docs/renders.md); the Linux ALSA live driver (the one
         permitted dependency: libasound)
test/    assert-based core, hosted-boundary and MIDI-dispatch tests;
         two-run FNV-64 render-signature determinism; SMF fuzz entrypoint
docs/    design notes, pinned constants, per-milestone evidence

Policy

• The core takes no third-party code; drivers may link platform libraries when a real capability demands it. libc and POSIX getopt are standard, not dependencies. See docs/design.md for the full policy.

Targets

Any Linux/ALSA box for development; the instrument target is a Linux SBC (Raspberry Pi 3B-class, aarch64).

License

MIT — see LICENSE. Free to use, modify, and distribute, including commercially, with attribution.