reaper-control/.sdd/changes/presets-pack/proposal.md

Proposal: presets-pack

Intent

All plugins use the SAME flat preset regardless of track role (bass/lead/chords/pad) or genre context. A Serum_2 on a bass track gets the same sound as Serum_2 on a lead track. Professional reggaeton needs role-specific timbres: deep sine 808 for bass, detuned saw for lead, warm pad for chords, evolving texture for pad. Same for FX: Decapitator on drums needs aggressive drive, on bass needs subtle warmth.

Scope

In Scope

• Restructure PLUGIN_PRESETS from flat {plugin: [chunks]} to role-aware {plugin: {role: [chunks]}}
• Create role-specific presets for plugins used in multiple roles: Serum_2 (bass/lead), Omnisphere (chords/pad), Decapitator (drums/bass)
• Programmatically derive new presets by base64-decoding existing presets (Serum=JSON, SoundToys=key=value), modifying genre-specific parameters, re-encoding
• Update make_plugin() in compose.py and _build_plugin() in __init__.py to resolve role-aware presets
• Add fallback: if no role-specific preset exists, use existing default preset

Out of Scope

• Creating presets from scratch in REAPER (requires GUI — can't programmatically)
• ReaScript-based preset capture (Phase 2)
• Presets for all 113 plugins — only multi-role targets initially
• Pro-Q 3 reggaeton EQ curve (no decodable format available)

Capabilities

New Capabilities

• presets-pack: Role-specific plugin preset resolution and preset data management

Modified Capabilities

None — existing plugin resolution unchanged; backward-compatible fallback to default preset.

Approach

Option B — Programmatic modification of decodable presets:

1. Serum_2: Decode base64 → JSON. Serum preset JSON has component: "processor" block with oscillator/wavetable/filter data. Create variants by modifying oscillator type (sine for bass, saw for lead), filter cutoff, envelope settings. Re-encode.

2. Decapitator (SoundToys): Decode base64 → key=value text (WIDGET = Decapitator;...). Create "aggressive" (high Drive, Tone bright) for drums, "warm" (low Drive, Tone dark) for bass. Re-encode.

3. Omnisphere: Decode base64 → SynthMaster text block. Create "warm pad" variant with slow attack, filter modulation; "evolving texture" with movement/LFO. Re-encode.

No GUI or REAPER needed — pure Python string processing over decoded preset text.

Affected Areas

Area	Impact	Description
src/reaper_builder/__init__.py	Modified	PLUGIN_PRESETS restructured; _build_plugin() accepts role param
src/composer/templates.py	Modified	_parse_vst_block(), make_plugin() resolution updated
scripts/compose.py	Modified	make_plugin() passes role; FX_CHAINS keys used for role
src/core/schema.py	Unchanged	PluginDef already has preset_data field

Risks

Risk	Likelihood	Mitigation
Modified preset crashes plugin on load	Low	Each variant derived from working ground-truth preset; only tweak known-safe params
Base64 decode/re-encode breaks binary integrity	Low	Round-trip test per plugin: decode → encode → bytes equal
Omnisphere text format undocumented	Med	Preserve structure, only modify known ATTRIBUTE values visible in decoded text

Rollback Plan

Revert PLUGIN_PRESETS to flat dict. Remove role param from _build_plugin() and make_plugin(). Existing tests verify preset injection still works.

Dependencies

• data/sample_index.json (independent — not affected)
• Existing ground-truth presets in PLUGIN_PRESETS (source material for variants)

Success Criteria

• python scripts/compose.py --bpm 99 --key Am produces .rpp where Serum_2 on bass track has different preset data than Serum_2 on lead track
• 110 existing tests continue to pass (backward-compatible fallback)
• Round-trip test: decode → modify → encode produces valid base64 matching original length structure
• At least 3 (plugin, role) combinations have distinct preset variants