Further tuning for AEC3 for initial echo suppression and handling of echo path changes

webrtc/modules/audio_processing/aec3/power_echo_model.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.
  */
 #include "webrtc/modules/audio_processing/aec3/power_echo_model.h"
@@ skipping 10 matching lines @@
 void RecentMaximum(const FftBuffer& X_buffer,
                    std::array<float, kFftLengthBy2Plus1>* R2) {
   R2->fill(0.f);
   for (size_t j = 0; j < 20; ++j) {
     std::transform(R2->begin(), R2->end(), X_buffer.Spectrum(j).begin(),
                    R2->begin(),
                    [](float a, float b) { return std::max(a, b); });
   }
 }
 
-constexpr float kHInitial = 10.f;
+constexpr float kHInitial = 100.f;

[peah-webrtc, 2017/02/27 14:26:03]

An echo path can often have a gain of 20 dB so 10 dB was too small for an
initial gain.

 constexpr int kUpdateCounterInitial = 300;
 
 }  // namespace
 
 PowerEchoModel::PowerEchoModel() {
   H2_.fill(CountedFloat(kHInitial, kUpdateCounterInitial));
 }
 
 PowerEchoModel::~PowerEchoModel() = default;
 
@@ skipping 60 matching lines @@
     std::transform(new_H2.begin(), new_H2.end(), H2_.begin(), H2_.begin(),
                    H2_updater);
   }
 
   // S2 = H2*X2_active.
   std::transform(H2_.begin(), H2_.end(), X2_active.begin(), S2->begin(),
                  [](CountedFloat a, float b) { return a.value * b; });
 }
 
 }  // namespace webrtc