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renato97 014e636889 feat: professional reggaeton production engine — 7 SDD changes, 302 tests

- section-energy: track activity matrix + volume/velocity multipliers per section
- smart-chords: ChordEngine with voice leading, inversions, 4 emotion modes
- hook-melody: melody engine with hook/stabs/smooth styles, call-and-response
- mix-calibration: Calibrator module (LUFS volumes, HPF/LPF, stereo, sends, master)
- transitions-fx: FX track with risers/impacts/sweeps at section boundaries
- sidechain: MIDI CC11 bass ducking on kick hits via DrumLoopAnalyzer
- presets-pack: role-aware plugin presets (Serum/Decapitator/Omnisphere per role)

Full SDD pipeline (propose→spec→design→tasks→apply→verify) for all 7 changes.
302/302 tests passing.

2026-05-03 23:54:29 -03:00

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Design: Transitions FX

Technical Approach

Add build_fx_track() to scripts/compose.py that places audio FX clips from the sample library at 7 section boundaries. Uses SampleSelector.select_one(role="fx") with per-type character hints. Reuses ClipDef.fade_in/out. New track inserted after Clap, before Pad — after main tracks, before sends are wired.

Architecture Decisions

Decision	Choice	Rejected	Rationale
One FX track vs per-section	Single dedicated track	Per-section tracks	Simpler; one import per sample in REAPER; manageable clip count (7–9)
Sample selection	Weighted random top-5	Pinned specific files	Variety across runs; selector scoring already works
Boundary timing	Hardcoded beat-offset map	Audio analysis	Section structure is deterministic; bar counts are fixed
Riser+impact at chorus	Two clips, same boundary	Single combined clip	Requires different timing; riser before boundary, impact on it

Data Flow

SECTIONS → offsets (bar → beat)
         │
         ▼
FX_TRANSITIONS map: {boundary_idx: (type, start_offset, length, fade_in, fade_out)}
         │
         ▼
build_fx_track(sections, offsets, selector, seed)
  ├── for each entry in FX_TRANSITIONS:
  │     ├── boundary_beat = offsets[boundary_idx] * 4
  │     ├── position = boundary_beat + start_offset
  │     ├── sample = selector.select_one(role="fx", seed=seed+idx)
  │     └── ClipDef(position, length, audio_path, fade_in, fade_out)
         │
         ▼
TrackDef("Transition FX", volume=0.72, clips=[...], send_level={...})

Boundary → FX Map

#	Boundary	Beat	FX Type	Position	Length	Fade In	Fade Out
2	verse→build	48	sweep	46	2	0.3	0.0
3	build→chorus	64	riser	60	4	1.5	0.0
3	build→chorus	64	impact	64	2	0.0	0.3
4	chorus→verse2	96	transition	94	2	0.2	0.2
5	verse2→chorus2	128	riser	124	4	1.0	0.0
6	chorus2→bridge	160	sweep	158	2	0.2	0.2
7	bridge→final	176	riser	172	4	1.0	0.0
8	final→outro	208	sweep	206	2	0.3	0.5

File Changes

File	Action	Description
`scripts/compose.py`	Modify	Add `FX_TRANSITIONS` dict + `build_fx_track()` (~50 lines); call in `main()` after clap track, before return tracks

Key Implementation Detail

SampleSelector.select_one() has a seed kwarg — new in the selector API. If not yet supported, use select(role="fx", limit=5) with manual random.choice(). Since FX is in ATONAL_ROLES, key compatibility scoring is skipped (neutral 0.5).

Track Ordering

tracks = [
    build_drumloop_track(...),    # 0
    build_perc_track(...),        # 1
    build_bass_track(...),        # 2
    build_chords_track(...),      # 3
    build_lead_track(...),        # 4
    build_clap_track(...),        # 5
    build_fx_track(...),          # 6 ← NEW
    build_pad_track(...),         # 7
]
return_tracks = create_return_tracks()  # 8 (Reverb), 9 (Delay)

Send wiring applies to all non-return tracks automatically via existing loop. FX track sends: Reverb=0.08, Delay=0.05.

Testing Strategy

Layer	What	How
Unit	`build_fx_track` returns TrackDef with 8 clips	Mock selector via `SampleSelector.__init__` patching
Unit	Clip positions match boundary map	Assert `clip.position` values equal expected beats
Integration	End-to-end .rpp output	`compose.py --bpm 99 --key Am --output test.rpp`; grep for "Transition FX" `<TRACK` block
Existing	110 tests pass	`pytest` before/after regression

Open Questions

None — all dependencies exist today (SampleSelector, ClipDef.fade_in/out, SECTIONS structure).

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