Add algorithm for Residual Echo Detector.

webrtc/modules/audio_processing/echo_detector/echo_detector.cc

Index: webrtc/modules/audio_processing/echo_detector/echo_detector.cc
diff --git a/webrtc/modules/audio_processing/echo_detector/echo_detector.cc b/webrtc/modules/audio_processing/echo_detector/echo_detector.cc
index 842be9e2db3a5a999de4dd07c02c40ec41c879db..a7c344e302a0fc1f320fc30667bb70af181a974a 100644
--- a/webrtc/modules/audio_processing/echo_detector/echo_detector.cc
+++ b/webrtc/modules/audio_processing/echo_detector/echo_detector.cc
@@ -10,21 +10,75 @@
 
 #include "webrtc/modules/audio_processing/echo_detector/echo_detector.h"
 
+#include <algorithm>
+#include <numeric>
+
+namespace {
+
+float Power(const rtc::ArrayView<const float>& input) {

[hlundin-webrtc, 2016/10/17 18:49:40]

Pass the ArrayView by value, not as ref.

[ivoc, 2016/10/18 15:20:19]

Done.

+  return std::inner_product(input.begin(), input.end(), input.begin(), 0.f);
+}
+
+}  // namespace
+
 namespace webrtc {
 
-void EchoDetector::BufferFarend(const rtc::ArrayView<const float>& /*farend*/) {
-  // TODO(ivoc): Add implementation.
-  RTC_NOTREACHED();
+EchoDetector::EchoDetector() = default;
+
+EchoDetector::~EchoDetector() = default;
+
+constexpr size_t EchoDetector::kLookbackFrames;
+constexpr size_t EchoDetector::kRenderBufferSize;
+
+void EchoDetector::BufferRender(const rtc::ArrayView<const float>& render) {
+  float power = Power(render);
+  render_buffer_.Insert(power);
 }
 
-void EchoDetector::Process(const rtc::ArrayView<const float>& /*nearend*/) {
-  // TODO(ivoc): Add implementation.
-  RTC_NOTREACHED();
+void EchoDetector::Process(const rtc::ArrayView<const float>& nearend) {
+  const float capture_power = Power(nearend);
+  capture_variance_.UpdateEstimate(capture_power);
+  const float capture_mean = capture_variance_.mean();
+  const float capture_std_deviation = capture_variance_.std_deviation();
+  echo_likelihood_ = 0.f;
+
+  const float latest_render_power = render_buffer_.GetValue();
+  render_variance_.UpdateEstimate(latest_render_power);
+  render_power_[next_insertion_index_] = latest_render_power;
+  render_power_mean_[next_insertion_index_] = render_variance_.mean();
+  render_power_std_dev_[next_insertion_index_] =
+      render_variance_.std_deviation();
+  for (size_t delay = 0; delay < covariance_.size(); ++delay) {
+    const size_t read_index =
+        (kLookbackFrames + next_insertion_index_ - delay) % kLookbackFrames;
+    RTC_DCHECK_LT(read_index, render_power_.size());
+    const float render_power = render_power_[read_index];
+    const float render_mean = render_power_mean_[read_index];
+    const float render_std_dev = render_power_std_dev_[read_index];
+    covariance_[delay].UpdateCovarianceEstimate(
+        capture_power, capture_mean, capture_std_deviation, render_power,
+        render_mean, render_std_dev);
+    echo_likelihood_ = std::max(
+        echo_likelihood_, covariance_[delay].normalized_cross_correlation());
+  }
+  // Update the next insertion index.
+  ++next_insertion_index_;
+  next_insertion_index_ %= kLookbackFrames;
+  RTC_DCHECK_LT(next_insertion_index_, kLookbackFrames);

[hlundin-webrtc, 2016/10/17 18:49:40]

DCHECKing immediately after the modulo is maybe not the most important. Consider
moving this DCHECK to before the index is used in line 47 instead. This will
make sure that it is not tampered with _somewhere else_ before being used next
time.

[ivoc, 2016/10/18 15:20:19]

Good idea.

 }
 
-void EchoDetector::Initialize(int /*sample_rate_hz*/) {
-  // TODO(ivoc): Add implementation.
-  RTC_NOTREACHED();
+void EchoDetector::Initialize() {
+  render_buffer_.Clear();
+  std::fill(render_power_.begin(), render_power_.end(), 0.f);
+  std::fill(render_power_mean_.begin(), render_power_mean_.end(), 0.f);
+  std::fill(render_power_std_dev_.begin(), render_power_std_dev_.end(), 0.f);
+  render_variance_.Clear();
+  capture_variance_.Clear();
+  for (auto& cov : covariance_) {
+    cov.Clear();
+  }
+  echo_likelihood_ = 0.f;
+  next_insertion_index_ = 0;
 }
 
 }  // namespace webrtc