fix(mq_editor): fuse spread_above/below into single spread param

Asymmetric spread offset the pitch center. Replace with a single
symmetric `spread` in harmonics config. autodetectSpread now returns
max(above, below). Update all defaults, UI, comments, and README.

handoff(Gemini): spread is now a single param; no compat shims.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

1 files changed, 11 insertions, 14 deletions

diff --git a/tools/mq_editor/editor.js b/tools/mq_editor/editor.js
index b07664e..98c92e5 100644
--- a/tools/mq_editor/editor.js
+++ b/tools/mq_editor/editor.js
@@ -124,7 +124,7 @@ class PartialEditor {
     const grid = this._synthGrid;
     grid.innerHTML = '';
 
-    const harmDefaults = { decay: 0.0, freq_mult: 2.0, jitter: 0.05, spread_above: 0.02, spread_below: 0.02 };
+    const harmDefaults = { decay: 0.0, freq_mult: 2.0, jitter: 0.05, spread: 0.02 };
     const resDefaults  = { r: 0.995, gainComp: 1.0 };
 
     const isResonator = !!(partial.resonator && partial.resonator.enabled);
@@ -158,11 +158,10 @@ class PartialEditor {
 
     const harm = partial.harmonics || {};
     const sinParams = [
-      { key: 'decay',        label: 'h.decay',  step: '0.01', max: '0.90' },
-      { key: 'freq_mult',    label: 'h.freq',   step: '0.01'  },
-      { key: 'jitter',       label: 'jitter',   step: '0.001' },
-      { key: 'spread_above', label: 'spread ↑', step: '0.001' },
-      { key: 'spread_below', label: 'spread ↓', step: '0.001' },
+      { key: 'decay',     label: 'h.decay', step: '0.01', max: '0.90' },
+      { key: 'freq_mult', label: 'h.freq',  step: '0.01'  },
+      { key: 'jitter',    label: 'jitter',  step: '0.001' },
+      { key: 'spread',    label: 'spread',  step: '0.001' },
     ];
     const sinInputs = {};
     for (const p of sinParams) {
@@ -206,22 +205,20 @@ class PartialEditor {
 
     // Auto-detect spread button
     const autoLbl = document.createElement('span');
-    autoLbl.textContent = 'spread';
+    autoLbl.textContent = '';
     const autoBtn = document.createElement('button');
-    autoBtn.textContent = 'Auto';
-    autoBtn.title = 'Infer spread_above/below from frequency variance around the bezier curve';
+    autoBtn.textContent = 'Auto spread';
+    autoBtn.title = 'Infer spread from half-power bandwidth around the bezier curve';
     autoBtn.addEventListener('click', () => {
       if (!this.partials) return;
       const p = this.partials[index];
       const sc = this.viewer ? this.viewer.stftCache : null;
       const sr = this.viewer ? this.viewer.audioBuffer.sampleRate : 44100;
       const fs = sc ? sc.fftSize : 2048;
-      const {spread_above, spread_below} = autodetectSpread(p, sc, fs, sr);
+      const {spread} = autodetectSpread(p, sc, fs, sr);
       if (!p.harmonics) p.harmonics = { ...harmDefaults };
-      p.harmonics.spread_above = spread_above;
-      p.harmonics.spread_below = spread_below;
-      sinInputs['spread_above'].value = spread_above.toFixed(4);
-      sinInputs['spread_below'].value = spread_below.toFixed(4);
+      p.harmonics.spread = spread;
+      sinInputs['spread'].value = spread.toFixed(4);
     });
     sinSection.appendChild(autoLbl);
     sinSection.appendChild(autoBtn);