refactor: optimize noise gate response time and introduce a gain floor for more natural background audio processing

app.py

@@ -151,18 +151,21 @@ def post_process_audio(
     if treble_gain != 0:
         waveform = F_audio.equalizer_biquad(waveform, sample_rate=sr, center_freq=6000.0, gain=treble_gain, Q=0.707)
 
-    # 4. Soft Noise Gate to remove background gating/watery artifacts during silence
+    # 4. Soft Noise Gate with a floor to keep background noise natural and not too dry
     if gate_threshold > -60.0:
         threshold = 10 ** (gate_threshold / 20.0)
         envelope = waveform.abs()
-        # Smooth envelope using 50ms average pooling
-        win_size = int(sr * 0.05)
+        # Fast 15ms window to open instantly at the start of words (avoids muddy onset delay)
+        win_size = int(sr * 0.015)
         if win_size % 2 == 0:
             win_size += 1
         env_padded = torch.nn.functional.pad(envelope, (win_size//2, win_size//2), mode='reflect')
         env_smooth = torch.nn.functional.avg_pool1d(env_padded.unsqueeze(0), kernel_size=win_size, stride=1).squeeze(0)
         # Soft sigmoid gating to prevent clicking
-        gain = torch.sigmoid((env_smooth - threshold) / (threshold * 0.25))
+        raw_gain = torch.sigmoid((env_smooth - threshold) / (threshold * 0.25))
+        # Keep a floor of 35% gain (approx -9dB) so background noise remains continuous & controllable
+        gate_floor = 0.35
+        gain = gate_floor + (1.0 - gate_floor) * raw_gain
         waveform = waveform * gain
 
     # 5. Analog Warmth (Soft Saturation / Tube Limiting)
@@ -248,10 +251,11 @@ def demo_fn(
 
     # Apply professional post-processing (Low-cut filter + bass EQ + treble EQ + gate + warmth) using optimized studio defaults
     if vocal_polish:
+        # We set low_cut_freq=110.0 to cut muddy frequency spikes at the start of words
         enhanced = post_process_audio(
             enhanced,
             sr,
-            low_cut_freq=80.0,
+            low_cut_freq=110.0,
             bass_gain=0.0,
             treble_gain=3.0,
             gate_threshold=-45.0,