Fix PhaseB live fbank normalization

app.js

@@ -14,7 +14,7 @@ const HOP_LENGTH = 160;
 const N_MELS = 80;
 const FIXED_FRAMES = 2005;
 const OUTPUT_STRIDE = 8;
-const PREEMPHASIS = 0.97;
+const PREEMPHASIS = 0.0;
 const CENTER_PAD = N_FFT / 2;
 const WINDOW_OFFSET = (N_FFT - WIN_LENGTH) / 2;
 const LOG_ZERO_GUARD = 2 ** -24;
@@ -257,6 +257,20 @@ function pcmToLogMel(pcm) {
     }
   }
 
+  for (let m = 0; m < N_MELS; m++) {
+    const offset = m * FIXED_FRAMES;
+    let mean = 0;
+    for (let t = 0; t < frameCount; t++) mean += features[offset + t];
+    mean /= frameCount;
+    let variance = 0;
+    for (let t = 0; t < frameCount; t++) {
+      const d = features[offset + t] - mean;
+      variance += d * d;
+    }
+    const scale = 1 / Math.sqrt(variance / frameCount + 1e-5);
+    for (let t = 0; t < frameCount; t++) features[offset + t] = (features[offset + t] - mean) * scale;
+  }
+
   return { features, frameCount };
 }