206 lines
7.2 KiB
Markdown
206 lines
7.2 KiB
Markdown
# Design: reggaeton-composer
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## Technical Approach
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Extend the existing `SongDefinition → FLPBuilder` pipeline with a new selection +
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melodic-generation layer. `SampleSelector` wraps `sample_index.json`; melodic
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generators produce `{notes, sample_path}` dicts; `SongDefinition` gains a
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`melodic_tracks` field; `FLPBuilder` appends audio-clip channels after existing
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drum channels.
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---
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## Architecture Decisions
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| Decision | Choice | Rejected | Rationale |
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|----------|--------|----------|-----------|
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| Selector load strategy | Load full index once at `__init__` | Lazy / streaming | 862 entries ≈ 50 MB max; random access needed for scoring |
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| Note format | Reuse `{"pos","len","key","vel"}` from `rhythm.py` | New format | Already converted by `_convert_rhythm_notes`; zero friction |
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| Schema extension | Add `melodic_tracks: list[MelodicTrack]` optional field | Separate class | Single source of truth; existing `validate()` extended, not replaced |
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| Channel numbering | Melodic starts at ch 17 | Dynamic | `skeleton.py` already defines `EMPTY_SAMPLER_CHANNELS = {17,18,19}`; expanding naturally |
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| Melodic channel type | `ChType = 21` → value `0` (sampler) | AudioClip type 1 | Reference FLP uses sampler channels for .wav; `skeleton.py` already patches them via `melodic_map` param (already present in `load()` signature) |
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| Builder integration | `_build_melodic_channels()` inserted between channel_bytes and arrangement | New Builder subclass | Minimal diff; builder is not subclassed anywhere |
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| CLI | `scripts/compose_track.py` using `argparse` | Click | Existing scripts use plain argparse |
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---
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## Data Flow
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```
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data/sample_index.json
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│
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▼
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SampleSelector.select(role, key, bpm, character, is_tonal)
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│ list[SampleEntry]
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▼
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melodic.py generators
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generate_bass / generate_lead / generate_chords / generate_pad
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│ MelodicTrackDef {role, sample_path, notes[], channel_hint}
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▼
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SongDefinition (extended)
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.melodic_tracks: list[MelodicTrack]
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│
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▼
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FLPBuilder.build(song)
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├── _build_header (unchanged)
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├── _build_all_patterns (unchanged)
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├── ChannelSkeletonLoader (pass melodic_map → already supported)
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├── _build_melodic_notes() (NEW — PatNotes for ch 17+)
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└── _build_arrangement (unchanged)
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│
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▼
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output/my_track.flp
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```
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---
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## File Changes
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| File | Action | Description |
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|------|--------|-------------|
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| `src/selector/__init__.py` | Create | `SampleSelector` class |
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| `src/composer/melodic.py` | Create | `generate_bass/lead/chords/pad` |
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| `src/flp_builder/schema.py` | Modify | Add `MelodicTrack`, `Note` dataclasses; extend `SongDefinition`; extend `validate()` and `from_json()` |
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| `src/flp_builder/builder.py` | Modify | Add `_build_melodic_notes()`; pass `melodic_map` to `ChannelSkeletonLoader.load()` |
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| `scripts/compose_track.py` | Create | CLI entry point |
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---
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## Interfaces / Contracts
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```python
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# src/selector/__init__.py
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@dataclass
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class SampleEntry:
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path: str # original_path (absolute)
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role: str
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key: str | None
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bpm: float # 0 = unknown
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character: str
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is_tonal: bool
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score: float = 0.0
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class SampleSelector:
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def __init__(self, index_path: str | Path): ...
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def select(
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self,
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role: str,
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key: str | None = None,
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bpm: float | None = None,
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character: str | None = None,
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is_tonal: bool | None = None,
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limit: int = 10,
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) -> list[SampleEntry]: ...
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# src/composer/melodic.py
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@dataclass
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class MelodicTrackDef:
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role: str # "bass" | "lead" | "chords" | "pad"
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sample_path: str
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notes: list[dict] # {"pos","len","key","vel"}
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channel_hint: int # suggested channel index (17+)
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def generate_bass(key, scale, bpm, bars, kick_pattern=None, density=0.7) -> MelodicTrackDef
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def generate_lead(key, scale, bpm, bars, density=0.5) -> MelodicTrackDef
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def generate_chords(key, scale, bpm, bars, progression=None, voicing="closed") -> MelodicTrackDef
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def generate_pad(key, scale, bpm, bars) -> MelodicTrackDef
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# src/flp_builder/schema.py (additions)
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_KNOWN_ROLES = frozenset({"bass","lead","chords","pad","arp","fx"})
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@dataclass
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class Note: # alias for PatternNote — same fields
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pos: float
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len: float
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key: int
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vel: int
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@dataclass
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class MelodicTrack:
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role: str
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sample_path: str
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notes: list[Note]
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channel_index: int # >= 17
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volume: float = 0.78 # 0.0–1.0
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pan: float = 0.0 # -1.0–1.0
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# SongDefinition gets:
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melodic_tracks: list[MelodicTrack] = field(default_factory=list)
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```
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---
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## Key Scoring Logic
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```python
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# Key compatibility (circle-of-fifths aware)
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COMPAT = {
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"exact": 1.0,
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"relative": 0.8, # Am ↔ C, Gm ↔ Bb
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"dominant": 0.6, # Am → Em
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"subdominant": 0.6, # Am → Dm
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"parallel": 0.5, # Am ↔ A
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}
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# Character groups (fuzzy matching)
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CHAR_GROUPS = [
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{"warm","soft","lush"},
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{"boomy","deep"},
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{"sharp","crisp","bright"},
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{"aggressive","dark"},
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]
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# Combined score = key_score * 0.5 + bpm_score * 0.3 + char_score * 0.2
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```
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---
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## Tresillo / Dembow Bass Pattern
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```
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Bar positions (8 bars × 4 beats = 32 beats):
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Tresillo: [0, 0.75, 1.5] per bar (3+3+2 in 8th-note grid)
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Kick-avoidance: skip notes within ±0.125 beats of a kick hit
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```
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---
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## Validation Extensions
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`SongDefinition.validate()` additions:
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1. `melodic_track.role in _KNOWN_ROLES`
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2. `Path(melodic_track.sample_path).exists()`
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3. `melodic_track.channel_index >= 17`
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4. No duplicate `channel_index` across melodic tracks
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---
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## Error Handling Strategy
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| Layer | Strategy |
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|-------|----------|
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| `SampleSelector.select()` | Returns `[]` on no match — callers must check; never raises on empty |
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| `generate_*` functions | Raise `ValueError` if `selector.select()` returns empty (required sample missing) |
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| `SongDefinition.validate()` | Accumulate all errors, raise `ValueError` with full list |
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| `FLPBuilder.build()` | Propagates `FileNotFoundError` if `sample_path` missing at write time |
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| CLI | `sys.exit(1)` with human-readable message on any `ValueError` / `FileNotFoundError` |
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---
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## Testing Strategy
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| Layer | What | Approach |
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|-------|------|----------|
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| Unit | `SampleSelector` scoring | Fixture with 5 hand-crafted entries; assert rank order |
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| Unit | `generate_bass` tresillo | Assert note positions match `[0, 0.75, 1.5]` per bar |
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| Unit | `MelodicTrack` schema validation | `validate()` returns expected errors for bad inputs |
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| Integration | `FLPBuilder` with melodic tracks | Build to bytes, parse header, assert `num_channels == 17 + n` |
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| Smoke | CLI end-to-end | `compose_track.py --key Am --bpm 95 --output /tmp/test.flp`; assert file exists and size > 0 |
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---
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## Open Questions
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- [ ] `skeleton.py` `EMPTY_SAMPLER_CHANNELS` includes `{17,18,19}` — need to confirm that adding melodic channels beyond 19 doesn't require reference FLP changes or if we expand the sampler clone range.
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- [ ] `sample_index.json` entries use `original_path` (absolute Windows paths). CLI on other machines will break. Decision needed: embed relative paths or make selector rebase paths against a configurable `library_root`.
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