feedback_/fbzm1_/fb_smooth_alpha_ were read every process() call but nothing
ever wrote feedback_, so the path was silently inert. Git history shows this
was a *muted* feature, not dead code: `feedback = v0 * feedbackGain` with
feedbackGain 0.1f (MEMLCeliumAudioApp.hpp @ d095688), then "0; //0.1f" —
zeroed with the value kept in the comment — then the write was dropped
entirely when the engine was ported to nisps/engines/ at the 2026-04-29
rewrite (8d0d47b). Operator decision: port it back, live at 0.1f.
The tap is voice 0's own enveloped output, post-envelope and pre voice-1/mix/
shape — NOT the final output. This differs from PAFSynth's feedback shape;
where the sibling and the reference disagreed, the reference won.
Not schema-exposed: the reference hardcoded it, and MEMLCelium has no voice
spaces to vary it by. If feedback depth becomes a research axis it wants to be
a runtime parameter — noted, not built.
Verification, and a gap worth recording: parity-check.sh PASSES (max delta
2.38e-7) but that is NOT evidence for this change — its harness only exercises
PAFSynth and ChannelStrip, and the impulse baseline runs all-params-0.5, under
which voice 0's sequencer never triggers, so v0_env stays 0 and the new write
is 0 either way. That baseline is blind to this path, not a check on it. So it
was cross-checked directly instead: sequencer params forced to trigger early,
4800 samples native vs WASM through the nisps_engine_* C ABI —
native vs WASM max abs diff 1.19e-7 (tolerance 1e-5)
all 4800 samples nonzero, finite, max amplitude ~0.99 (tanh-bounded)
same run with gain forced to 0 diverges by up to 1.49 — not a no-op
No fixture regenerated. nisps.wasm ships here because it is a tracked artifact
under the Phase 0 freshness gate.
Follow-up: the parity harness covers 2 of 8 engines. "Firmware and WASM share
the same engines" is asserted repo-wide but tested narrowly.
Phase 3 (L8). Pure statement-for-statement relocation into
dsp/ratio_seq.hpp, dsp/seq_clock.hpp and core/event_queue.hpp.
AUDIT CORRECTION: L8 says "breakor and elysiamorf duplicate ratio_seq". That is
false — ElysiamorfEngine has no ratio_seq at all; it triggers continuously via
FM operators. The real duplicate pair is BreakOrEngine and MEMLCeliumEngine,
whose copies are byte-for-byte identical. Elysiamorf did share the clock and
event-queue machinery, so it uses those. memlcelium now includes the shared
ratio_seq too, which is what actually closes this finding.
Deliberately NOT folded into core/ring_buffer.hpp: RingBuffer is an
atomics-based cross-core SPSC channel (its header says so), whereas the engines'
event queue is produced and drained on one thread. Reusing it would have meant
paying for atomics to serve a single-threaded FIFO. The distinction is now
recorded in MAP.md so the next audit does not read them as duplicates.
Bit-exactness: verified the MIDI-clock tick and bar-phasor tick preserve the
original operation order with no floating-point re-association, and that
EventQueue keeps the original `% N` indexing rather than adopting RingBuffer's
bitmask. The golden suite (nisps_golden_tests) and the native<->WASM parity blob
both pass unchanged — they are the check, and they were not re-baselined.
Phase 1 group 3 (L3, L9, L4, L5, L6, ST1).
- L3: nisps/modes/voice_space.hpp — entirely dead, no includes anywhere.
- L4: deleted SawOsc and SquareOsc. KEPT SineOsc — a verifier caught that the
original reviewer's grep missed its live consumer (the firmware selftest);
re-confirmed here before touching the file.
- L9: removed the no-op VoiceSpace enum/table/setter boilerplate from the five
engines with no real voice spaces; kept it on PAFSynth, VerbFX and
ChannelStrip, which have real ones. Every engine member was checked against
nisps/wasm/bindings.cpp, firmware/ and tests/ for callers first.
- L5: ModeBase::input_dirty_ was write-only state — deleted the flag rather
than making it gate inference, which would have been a behaviour change.
- L6: VerbFXEngine's delay_to_verb_ (computed 12x per block, never read),
enable_reverb_, enable_delay_to_reverb_ and the unused set_enable_* setters.
- ST1: rewrote the four engine header comment blocks that described
implementations which do not exist.
L7 (MEMLCeliumEngine's inert feedback path) is deliberately NOT done — tracing
git history showed feedbackGain went 0.1f (live) -> "0; //0.1f" (explicitly
muted, value preserved) -> dropped entirely in the port. That is a muted
feature, not dead weight, and deleting it would silently lose it. Left intact
pending an operator decision; see the phase report.
Gates: run-all-tests.sh ALL GREEN.
Stream 3's NoOpEngine used engine_id()=='noop' but the schema for
sound_analysis_midi.json declares engine_id: 'thru' (matches firmware's
ThruAudioApp naming). The class name stays NoOpEngine — it accurately
describes what process() does — but the schema-facing identifier is now
'thru'. BreakOr/Elysiamorf compose NoOpEngine by type, not engine_id, so
they're unaffected.
