Major updates to the echo removal functionality in AEC3

webrtc/modules/audio_processing/aec3/comfort_noise_generator.cc

 /*
  *  Copyright (c) 2017 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 170 matching lines @@
         N2_initial_.reset();
       } else {
         // Compute the N2_initial from N2.
         std::transform(
             N2_.begin(), N2_.end(), N2_initial_->begin(), N2_initial_->begin(),
             [](float a, float b) { return a > b ? b + 0.001f * (a - b) : a; });
       }
     }
   }
 
+  // Limit the noise to a floor of -96 dBFS.
+  constexpr float kNoiseFloor = 440.f;
+  for (auto& n : N2_) {
+    n = std::max(n, kNoiseFloor);
+  }
+  if (N2_initial_) {
+    for (auto& n : *N2_initial_) {
+      n = std::max(n, kNoiseFloor);
+    }
+  }
+
   // Choose N2 estimate to use.
   const std::array<float, kFftLengthBy2Plus1>& N2 =
       N2_initial_ ? *N2_initial_ : N2_;
 
   switch (optimization_) {
 #if defined(WEBRTC_ARCH_X86_FAMILY)
     case Aec3Optimization::kSse2:
       aec3::EstimateComfortNoise_SSE2(N2, &seed_, lower_band_noise,
                                       upper_band_noise);
       break;
 #endif
     default:
       aec3::EstimateComfortNoise(N2, &seed_, lower_band_noise,
                                  upper_band_noise);
   }
 }
 
 }  // namespace webrtc