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, 9 insertions, 11 deletions

diff --git a/tools/mq_editor/mq_synth.js b/tools/mq_editor/mq_synth.js
index e5f7e1a..eeb3b00 100644
--- a/tools/mq_editor/mq_synth.js
+++ b/tools/mq_editor/mq_synth.js
@@ -26,7 +26,7 @@ function buildHarmonics(harmonics) {
 
 // Synthesize audio from MQ partials
 // partials: array of {freqCurve (with a0-a3 for amp), harmonics?, resonator?}
-// harmonics: {decay, freq_mult, jitter, spread_above, spread_below}
+// harmonics: {decay, freq_mult, jitter, spread}
 // resonator: {enabled, r, gainComp}  — two-pole resonator mode per partial
 // integratePhase: true = accumulate 2π*f/SR per sample (correct for varying freq)
 //                 false = 2π*f*t (simpler, only correct for constant freq)
@@ -37,11 +37,10 @@ function synthesizeMQ(partials, sampleRate, duration, integratePhase = true, opt
   const pcm = new Float32Array(numSamples);
 
   const defaultHarmonics = {
-    decay:        0.0,
-    freq_mult:    1.0,
-    jitter:       0.05,
-    spread_above: 0.02,
-    spread_below: 0.02
+    decay:     0.0,
+    freq_mult: 1.0,
+    jitter:    0.05,
+    spread:    0.02
   };
 
   // Pre-build per-partial configs with fixed spread/jitter and phase accumulators
@@ -78,17 +77,16 @@ function synthesizeMQ(partials, sampleRate, duration, integratePhase = true, opt
     } else {
       // --- Sinusoidal (harmonic) mode ---
       const harm = partial.harmonics || defaultHarmonics;
-      const spread_above = harm.spread_above ?? 0.0;
-      const spread_below = harm.spread_below ?? 0.0;
-      const jitter       = harm.jitter       ?? 0.0;
+      const spread = harm.spread ?? 0.0;
+      const jitter = harm.jitter ?? 0.0;
 
       const harmonicList = buildHarmonics(harm);
       const replicaData = [];
       for (let h = 0; h < harmonicList.length; ++h) {
         const hc        = harmonicList[h];
-        const spread    = randFloat(p * 67890 + h * 999, -spread_below, spread_above);
+        const spreadVal = randFloat(p * 67890 + h * 999, -spread, spread);
         const initPhase = randFloat(p * 67890 + h, 0.0, 1.0) * jitter * 2.0 * Math.PI;
-        replicaData.push({ ratio: hc.ratio, ampMult: hc.ampMult, spread, phase: initPhase });
+        replicaData.push({ ratio: hc.ratio, ampMult: hc.ampMult, spread: spreadVal, phase: initPhase });
       }
       configs.push({ mode: 'sinusoid', fc, replicaData });
     }