Major updates to the echo removal functionality in AEC3

webrtc/modules/audio_processing/aec3/shadow_filter_update_gain.cc

Index: webrtc/modules/audio_processing/aec3/shadow_filter_update_gain.cc
diff --git a/webrtc/modules/audio_processing/aec3/shadow_filter_update_gain.cc b/webrtc/modules/audio_processing/aec3/shadow_filter_update_gain.cc
index ee6938b31e805312c30952a16e6357ce7190f5df..85bc11fb0d631865cc45ec2e25b019aa047b3509 100644
--- a/webrtc/modules/audio_processing/aec3/shadow_filter_update_gain.cc
+++ b/webrtc/modules/audio_processing/aec3/shadow_filter_update_gain.cc
@@ -18,7 +18,7 @@
 namespace webrtc {
 
 void ShadowFilterUpdateGain::Compute(
-    const RenderBuffer& X_buffer,
+    const RenderBuffer& render_buffer,
     const RenderSignalAnalyzer& render_signal_analyzer,
     const FftData& E_shadow,
     size_t size_partitions,
@@ -40,12 +40,14 @@ void ShadowFilterUpdateGain::Compute(
   }
 
   // Compute mu.
-  constexpr float kX2Min = 44015068.0f;
+  // Corresponds to WGN of power -39 dBFS.
+  constexpr float kNoiseGatePower = 220075344.f;
   constexpr float kMuFixed = .5f;
   std::array<float, kFftLengthBy2Plus1> mu;
-  const auto& X2 = X_buffer.SpectralSum(size_partitions);
-  std::transform(X2.begin(), X2.end(), mu.begin(),
-                 [&](float a) { return a > kX2Min ? kMuFixed / a : 0.f; });
+  const auto& X2 = render_buffer.SpectralSum(size_partitions);
+  std::transform(X2.begin(), X2.end(), mu.begin(), [&](float a) {
+    return a > kNoiseGatePower ? kMuFixed / a : 0.f;
+  });
 
   // Avoid updating the filter close to narrow bands in the render signals.
   render_signal_analyzer.MaskRegionsAroundNarrowBands(&mu);