fix(editor): Apply window to spectrum before IDCT, not after

Fixed comb-like pattern in web editor playback by matching the C++
synth windowing strategy.

Root Cause:
- C++ synth (synth.cc): Applies window to SPECTRUM before IDCT
- JavaScript editors: Applied window to TIME DOMAIN after IDCT
- This mismatch caused phase/amplitude distortion (comb pattern)

Solution:
- Updated spectral_editor/script.js: Window spectrum before IDCT
- Updated editor/script.js: Window spectrum before IDCT
- Removed redundant time-domain windowing after IDCT
- JavaScript now matches C++ approach exactly

Result:
- Clean frequency spectrum (no comb pattern)
- Correct audio playback matching C++ synth output
- Generated Gaussian curves sound proper

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

2 files changed, 14 insertions, 7 deletions

diff --git a/tools/editor/script.js b/tools/editor/script.js
index abfd4f4..ebc543a 100644
--- a/tools/editor/script.js
+++ b/tools/editor/script.js
@@ -631,11 +631,18 @@ async function playSpectrogramData(specData) {
     // Convert spectrogram frames (frequency domain) to audio samples (time domain)
     for (let frameIndex = 0; frameIndex < numFrames; frameIndex++) {
         const spectralFrame = specData.data.slice(frameIndex * dctSize, (frameIndex + 1) * dctSize);
-        const timeDomainFrame = javascript_idct_512(spectralFrame);
 
-        // Apply Hanning window for smooth transitions
+        // Apply window to spectrum before IDCT (matches C++ synth.cc)
+        const windowedSpectral = new Float32Array(dctSize);
         for (let i = 0; i < dctSize; i++) {
-            audioData[frameIndex * dctSize + i] = timeDomainFrame[i] * hanningWindowArray[i];
+            windowedSpectral[i] = spectralFrame[i] * hanningWindowArray[i];
+        }
+
+        const timeDomainFrame = javascript_idct_512(windowedSpectral);
+
+        // Direct output (no additional windowing)
+        for (let i = 0; i < dctSize; i++) {
+            audioData[frameIndex * dctSize + i] = timeDomainFrame[i];
         }
     }
 
diff --git a/tools/spectral_editor/script.js b/tools/spectral_editor/script.js
index 4053aef..677a823 100644
--- a/tools/spectral_editor/script.js
+++ b/tools/spectral_editor/script.js
@@ -1543,20 +1543,20 @@ function spectrogramToAudio(spectrogram, dctSize, numFrames) {
     const window = hanningWindowArray;
 
     for (let frameIdx = 0; frameIdx < numFrames; frameIdx++) {
-        // Extract frame
+        // Extract frame and apply window to spectrum (matches C++ synth.cc)
         const frame = new Float32Array(dctSize);
         for (let b = 0; b < dctSize; b++) {
-            frame[b] = spectrogram[frameIdx * dctSize + b];
+            frame[b] = spectrogram[frameIdx * dctSize + b] * window[b];
         }
 
         // IDCT
         const timeFrame = javascript_idct_512(frame);
 
-        // Apply window and overlap-add
+        // Overlap-add (no additional windowing - window already applied to spectrum)
         const frameStart = frameIdx * hopSize;
         for (let i = 0; i < dctSize; i++) {
             if (frameStart + i < audioLength) {
-                audioData[frameStart + i] += timeFrame[i] * window[i];
+                audioData[frameStart + i] += timeFrame[i];
             }
         }
     }