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, 10 deletions

diff --git a/tools/mq_editor/mq_extract.js b/tools/mq_editor/mq_extract.js
index 47c21b9..0940cf1 100644
--- a/tools/mq_editor/mq_extract.js
+++ b/tools/mq_editor/mq_extract.js
@@ -270,13 +270,12 @@ function expandPartialsLeft(partials, frames) {
   }
 }
 
-// Autodetect spread_above / spread_below from the spectrogram.
-// For each (subsampled) STFT frame within the partial, measures the
-// half-power (-3dB) width of the spectral peak above and below the center.
-// spread = half_bandwidth / f0  (fractional).
+// Autodetect spread from the spectrogram.
+// Measures -3dB half-bandwidth above and below the peak in each STFT frame,
+// returns spread = max(above, below) / f0 as a fractional frequency offset.
 function autodetectSpread(partial, stftCache, fftSize, sampleRate) {
   const curve = partial.freqCurve;
-  if (!curve || !stftCache) return {spread_above: 0.02, spread_below: 0.02};
+  if (!curve || !stftCache) return {spread: 0.02};
 
   const numFrames = stftCache.getNumFrames();
   const binHz    = sampleRate / fftSize;
@@ -331,9 +330,9 @@ function autodetectSpread(partial, stftCache, fftSize, sampleRate) {
     ++count;
   }
 
-  const spread_above = count > 0 ? Math.sqrt(sumAbove / count) : 0.01;
-  const spread_below = count > 0 ? Math.sqrt(sumBelow / count) : 0.01;
-  return {spread_above, spread_below};
+  const sa = count > 0 ? Math.sqrt(sumAbove / count) : 0.01;
+  const sb = count > 0 ? Math.sqrt(sumBelow / count) : 0.01;
+  return {spread: Math.max(sa, sb)};
 }
 
 // Track a single partial starting from a (time, freq) seed position.
@@ -428,7 +427,7 @@ function trackFromSeed(frames, seedTime, seedFreq, params) {
   return {
     times: allTimes, freqs: allFreqs, amps: allAmps, phases: allPhases,
     muted: false, freqCurve,
-    harmonics: { decay: 0.0, freq_mult: 2.0, jitter: 0.05, spread_above: 0.02, spread_below: 0.02 },
+    harmonics: { decay: 0.0, freq_mult: 2.0, jitter: 0.05, spread: 0.02 },
   };
 }
 
@@ -522,7 +521,7 @@ function trackIsoContour(stftCache, seedTime, seedFreq, params) {
     times: allTimes, freqs: allFreqs, amps: allAmps,
     phases: new Array(allTimes.length).fill(0),
     muted: false, freqCurve,
-    harmonics: { decay: 0.0, freq_mult: 2.0, jitter: 0.05, spread_above: 0.15, spread_below: 0.15 },
+    harmonics: { decay: 0.0, freq_mult: 2.0, jitter: 0.05, spread: 0.15 },
   };
 }