diff --git a/CLAUDE.md b/CLAUDE.md
index 2bcfc3b..b0b3b59 100644
--- a/CLAUDE.md
+++ b/CLAUDE.md
@@ -28,12 +28,32 @@ See `nisps-core/README.md` for complete documentation and examples.
 
 The `playground/` directory contains a browser-based interactive demo of the NISPS ML engine. It's a faithful JavaScript port of nisps-core's MLP + IML, with no build step or dependencies.
 
-- **2 inputs** (virtual joystick X/Y) mapped through a `[3, 10, 10, 14, 20]` MLP to **20 outputs** controlling a Canvas2D flow-field particle system
+- **2 inputs** (virtual joystick X/Y) mapped through a `[3, 32, 48, 64, 126]` MLP to **126 outputs**
+- **Two output modes**:
+  - **Visual**: first 20 outputs control a Canvas2D flow-field particle system
+  - **Synth (C15)**: all 126 outputs control the C15 WASM synthesizer — every sonically meaningful continuous parameter across envelopes, oscillators, shapers, filters, feedback/output mixers, cabinet, and effects
 - **Two learning modes**: Examples (set slider targets, add examples, train) and RL Feedback (thumbs up/down with exploration noise)
 - **Serve statically**: `cd playground && python3 -m http.server`
 - **Mobile-first**: designed for touch/foldable phone use
 
-Key files: `js/nisps/` (ML core port), `js/ui/` (visualizer, joystick, controls), `js/app.js` (wiring).
+Key files: `js/nisps/` (ML core port), `js/ui/` (visualizer, joystick, controls), `js/synth/` (C15 bridge, param map, arpeggiator), `js/app.js` (wiring).
+
+### C15 Parameter Map
+
+The 126 synth parameters in `js/synth/param-map.js` were curated from the C15's 287 total parameters. Excluded categories:
+
+| Excluded | Count | Reason |
+|----------|-------|--------|
+| Hardware Amount/Source | 56 | No physical MIDI hardware in browser |
+| Macro Controls/Times | 12 | Meta-routing layer conflicts with direct ML control |
+| Scale offsets | 13 | Microtuning would break pitch unpredictably |
+| Key tracking (`*_KT`) | 11 | Pitch-dependent scaling needs calibrated defaults |
+| Velocity (`*_Vel`) | 11 | Velocity-dependent, ML can't observe key velocity |
+| Envelope mod depths (`*_Env_A/B/C`) | 19 | Multiplicative interaction with envelope shapes makes space too hard to learn |
+| Discrete/structural | 15 | Osc Pitch (full sweep), Master Vol/Tune, Voice Mute/Fade, Unison Voices, Mono modes, Split, Osc Reset |
+| Secondary config | 7 | Att Curve, Elevate, Chirp, Decay Gate, Retrigger |
+| PM shaper blend | 4 | Secondary routing params |
+| FB Mix source selects | 4 | Discrete A/B selectors |
 
 ## Build System
 
diff --git a/playground/README.md b/playground/README.md
index 8ca2c04..993ef09 100644
--- a/playground/README.md
+++ b/playground/README.md
@@ -13,16 +13,30 @@ Run the command from the `playground/` directory.
 
 ## What it does
 
-- Maps 2D joystick input (X/Y) through an MLP to 20 visualization parameters.
-- Renders a flow-field particle visualization on a Canvas2D surface.
+- Maps 2D joystick input (X/Y) through an MLP (`[3, 32, 48, 64, 126]`) to 126 outputs.
+- **Visual mode**: first 20 outputs drive a flow-field particle visualization on Canvas2D.
+- **Synth mode (C15)**: all 126 outputs control the C15 WASM synthesizer — envelopes, oscillators, shapers, filters, feedback/output mixers, cabinet, and effects.
 - Supports two learning modes:
   - **Examples**: add explicit input/output pairs and train.
   - **RL Feedback**: give thumbs up/down while exploring outputs.
 
+## C15 synth parameters
+
+The 126 synth parameters (`js/synth/param-map.js`) cover all sonically meaningful continuous parameters of the C15 engine. Excluded from the C15's 287 total params:
+
+- Hardware routing (56) — no physical MIDI in browser
+- Macro controls (12) — conflicts with direct ML control
+- Scale/tuning (13) — would break pitch
+- Key tracking / velocity (22) — depend on note context ML can't observe
+- Envelope mod depths (19) — too many multiplicative interactions for 2-input ML
+- Discrete/structural/dangerous (19) — pitch sweep, volume, switches, resets
+- Secondary config (15) — curves, chirp, shaper blend, source selects
+
 ## UI controls
 
+- **Output mode tabs** (side panel): switch between Visual and Synth modes.
 - **Expand / Collapse** button on the canvas: makes the visual surface nearly full-screen and compresses lower controls into a minimal view.
-- **Presets**: quick demo mappings (`Calm/Chaos`, `Rainbow`, `Vortex`).
+- **Presets**: quick demo mappings (`Calm/Chaos`, `Rainbow`, `Vortex`) — visual mode only.
 - **Help** (`?`) overlay: in-app usage guide.
 - **Follow mode**: double-click joystick in RL mode to toggle no-hold interaction.
 - **Keyboard in Follow mode (RL)**: `2` = thumbs up, `1` = thumbs down.
@@ -35,3 +49,5 @@ Run the command from the `playground/` directory.
 - `js/app.js` - app wiring and interaction logic.
 - `js/ui/` - visualizer, joystick, controls, parameter display.
 - `js/nisps/` - JavaScript MLP + IML core.
+- `js/synth/` - C15 WASM bridge, parameter map, arpeggiator.
+- `c15/` - C15 engine WASM binary and parameter definitions.