Add a reliability term to the echo detector.

This will ensure that the estimated likelihood starts at a low value and prevents initial spikes.

BUG=webrtc:6525

Review-Url: https://codereview.webrtc.org/2503843004
Cr-Commit-Position: refs/heads/master@{#15131}

webrtc/modules/audio_processing/residual_echo_detector.cc

@@ -25,6 +25,7 @@ float Power(rtc::ArrayView<const float> input) {
 constexpr size_t kLookbackFrames = 650;
 // TODO(ivoc): Verify the size of this buffer.
 constexpr size_t kRenderBufferSize = 30;
+constexpr float kAlpha = 0.001f;
 
 }  // namespace
 
@@ -100,6 +101,8 @@ void ResidualEchoDetector::AnalyzeCaptureAudio(
     echo_likelihood_ = std::max(
         echo_likelihood_, covariances_[delay].normalized_cross_correlation());
   }
+  reliability_ = (1.0f - kAlpha) * reliability_ + kAlpha * 1.0f;
+  echo_likelihood_ *= reliability_;
   int echo_percentage = static_cast<int>(echo_likelihood_ * 100);
   RTC_HISTOGRAM_COUNTS("WebRTC.Audio.ResidualEchoDetector.EchoLikelihood",
                        echo_percentage, 0, 100, 100 /* number of bins */);
@@ -121,6 +124,7 @@ void ResidualEchoDetector::Initialize() {
   }
   echo_likelihood_ = 0.f;
   next_insertion_index_ = 0;
+  reliability_ = 0.f;
 }
 
 void ResidualEchoDetector::PackRenderAudioBuffer(

webrtc/modules/audio_processing/residual_echo_detector.h

@@ -37,6 +37,9 @@ class ResidualEchoDetector {
   // This function should be called while holding the capture lock.
   void Initialize();
 
+  // This function is for testing purposes only.
+  void SetReliabilityForTest(float value) { reliability_ = value; }
+
   static void PackRenderAudioBuffer(AudioBuffer* audio,
                                     std::vector<float>* packed_buffer);
 
@@ -71,6 +74,8 @@ class ResidualEchoDetector {
   MeanVarianceEstimator capture_statistics_;
   // Current echo likelihood.
   float echo_likelihood_ = 0.f;
+  // Reliability of the current likelihood.
+  float reliability_ = 0.f;
 };
 
 }  // namespace webrtc

webrtc/modules/audio_processing/residual_echo_detector_unittest.cc

@@ -17,6 +17,7 @@ namespace webrtc {
 
 TEST(ResidualEchoDetectorTests, Echo) {
   ResidualEchoDetector echo_detector;
+  echo_detector.SetReliabilityForTest(1.0f);
   std::vector<float> ones(160, 1.f);
   std::vector<float> zeros(160, 0.f);
 
@@ -41,6 +42,7 @@ TEST(ResidualEchoDetectorTests, Echo) {
 
 TEST(ResidualEchoDetectorTests, NoEcho) {
   ResidualEchoDetector echo_detector;
+  echo_detector.SetReliabilityForTest(1.0f);
   std::vector<float> ones(160, 1.f);
   std::vector<float> zeros(160, 0.f);
 
@@ -60,6 +62,7 @@ TEST(ResidualEchoDetectorTests, NoEcho) {
 
 TEST(ResidualEchoDetectorTests, EchoWithRenderClockDrift) {
   ResidualEchoDetector echo_detector;
+  echo_detector.SetReliabilityForTest(1.0f);
   std::vector<float> ones(160, 1.f);
   std::vector<float> zeros(160, 0.f);
 
@@ -94,6 +97,7 @@ TEST(ResidualEchoDetectorTests, EchoWithRenderClockDrift) {
 
 TEST(ResidualEchoDetectorTests, EchoWithCaptureClockDrift) {
   ResidualEchoDetector echo_detector;
+  echo_detector.SetReliabilityForTest(1.0f);
   std::vector<float> ones(160, 1.f);
   std::vector<float> zeros(160, 0.f);