Add algorithm for Residual Echo Detector.

webrtc/modules/audio_processing/echo_detector/echo_detector.h

Index: webrtc/modules/audio_processing/echo_detector/echo_detector.h
diff --git a/webrtc/modules/audio_processing/echo_detector/echo_detector.h b/webrtc/modules/audio_processing/echo_detector/echo_detector.h
index fd190834329cc1760208f0efd7349ab62e84fc62..f0a55fec74f99669ff7e9059ee30e3e231beebe3 100644
--- a/webrtc/modules/audio_processing/echo_detector/echo_detector.h
+++ b/webrtc/modules/audio_processing/echo_detector/echo_detector.h
@@ -12,19 +12,100 @@
 #define WEBRTC_MODULES_AUDIO_PROCESSING_ECHO_DETECTOR_ECHO_DETECTOR_H_
 
 #include <stddef.h>
+#include <vector>
 
 namespace webrtc {
 
+// This class iteratively estimates the mean and variance of a signal.
+class MeanVarianceEstimator {

[hlundin-webrtc, 2016/10/14 08:00:39]

This and the two next classes are an internal matter for EchoDetector. Either
make them internal to that one (hard to test, should only be done for more or
less trivial help classes) or declare and implement them in their own files
(preferred).

[ivoc, 2016/10/17 16:05:08]

Ok, I will move each to its own file.

+ public:
+  void UpdateEstimate(float value);
+  float SigmaEstimate();

[hlundin-webrtc, 2016/10/14 08:00:40]

const method

[hlundin-webrtc, 2016/10/14 08:00:40]

This is almost an accessor method; you can name it such: sigma_estimate(), or
std_deviation_estimate() since sigma is not used anywhere else in the class.

[peah-webrtc, 2016/10/14 08:18:58]

const

[ivoc, 2016/10/17 16:05:08]

Done, I went with std_deviation (without estimate) as a new name, to make it
more consistent with the new name of mean().

+  float MeanEstimate();

[hlundin-webrtc, 2016/10/14 08:00:40]

This is a simple accessor method => float mean() const;
And unless some style tool complains, I think it is fine to implement it here.

[peah-webrtc, 2016/10/14 08:18:58]

const

[ivoc, 2016/10/17 16:05:08]

Done.

+  void Clear();
+
+ private:
+  // Estimate of the expected value of the input values.
+  float mean_ = 0.f;
+  // Estimate of the variance of the input values.
+  float variance_ = 0.f;
+  // Parameter controlling the adaptation speed.
+  static constexpr float alpha_ = 0.01f;

[hlundin-webrtc, 2016/10/14 08:00:40]

static const members should go before variable members, and should be named
kAlpha.

[ivoc, 2016/10/17 16:05:08]

Done.

+};
+
+// This class iteratively estimates the covariance between two signals.
+class CovarianceEstimator {
+ public:
+  void UpdateCovarianceEstimate(float x,
+                                float x_mean,
+                                float x_var,
+                                float y,
+                                float y_mean,
+                                float y_var);
+  float PCCEstimate();

[hlundin-webrtc, 2016/10/14 08:00:39]

float pcc() const { return pcc_; }

[hlundin-webrtc, 2016/10/14 08:00:40]

Comment, so that the reader understands what PCC means.

[ivoc, 2016/10/17 16:05:08]

Done.

+  void Clear();
+
+ private:
+  // Estimate of the Pearson product-moment correlation coefficient of the two
+  // signals.
+  float PCC_ = 0.f;

[hlundin-webrtc, 2016/10/14 08:00:39]

pcc_

[ivoc, 2016/10/17 16:05:08]

I renamed this to normalized_cross_correlation_, following Per's suggestion.

+  // Estimate of the covariance value.
+  float covariance_ = 0.f;
+  // Parameter controlling the adaptation speed.
+  static constexpr float alpha_ = 0.01f;

[hlundin-webrtc, 2016/10/14 08:00:39]

Same comments as above: move up and rename to kAlpha.

[ivoc, 2016/10/17 16:05:08]

Done.

+};
+
+// Ring buffer containing floating point values.
+struct CircularBuffer {
+ public:
+  CircularBuffer(int size);

[hlundin-webrtc, 2016/10/14 08:00:39]

explicit

[hlundin-webrtc, 2016/10/14 08:00:40]

size_t size

[ivoc, 2016/10/17 16:05:08]

Done.

+  ~CircularBuffer();
+
+  void Insert(float value);
+  float GetValue(int delay);
+  void Clear();
+
+ private:
+  std::vector<float> buffer_;
+  const int size_;

[hlundin-webrtc, 2016/10/14 08:00:39]

const size_t

[peah-webrtc, 2016/10/14 08:18:58]

You don't need the size_ constant. Use buffer_.size() instead.

[ivoc, 2016/10/17 16:05:08]

I thought it would be more efficient to store it than to call the .size()
function repeatedly. Perhaps you're right that it's better to remove it (I guess
it is a premature optimization).

+  int next_insertion_index_ = 0;

[hlundin-webrtc, 2016/10/14 08:00:39]

size_t

[ivoc, 2016/10/17 16:05:08]

Done.

+};
+
 class EchoDetector {
  public:
-  EchoDetector() {}
-  ~EchoDetector() {}
+  EchoDetector();
+  ~EchoDetector();
 
   void BufferFarend(const float* farend, size_t num_samples);
 
   void Process(const float* nearend, size_t num_samples);
 
   void Initialize(int sample_rate_hz);
+
+  float EchoLikelihood();

[hlundin-webrtc, 2016/10/14 08:00:39]

float echo_likelihood() const { return echo_likelihood_; }

[ivoc, 2016/10/17 16:05:08]

Done.

+
+ private:
+  static constexpr int lookback_periods_ = 650;

[hlundin-webrtc, 2016/10/14 08:00:39]

kLookbackPeriods

[hlundin-webrtc, 2016/10/14 08:00:39]

size_t?

[peah-webrtc, 2016/10/14 08:18:58]

size_t?

[ivoc, 2016/10/17 16:05:08]

Done.

+  static constexpr int render_buffer_size_ = 20;

[hlundin-webrtc, 2016/10/14 08:00:39]

kRenderBufferSize

[hlundin-webrtc, 2016/10/14 08:00:40]

Definitely size_t.

[peah-webrtc, 2016/10/14 08:18:58]

size_t?

[ivoc, 2016/10/17 16:05:08]

Done.

+
+  // Buffer for storing the power of incoming farend buffers. This is needed for
+  // cases where calls to BufferFarend and Process are jittery.
+  CircularBuffer render_buffer_;
+  // Delay of next render sample that should be used.
+  int render_buffer_delay_ = 0;

[peah-webrtc, 2016/10/14 08:18:58]

size_t?

[ivoc, 2016/10/17 16:05:08]

Done.

+
+  // Delayed versions of the power, mean and sigma, for calculating the delayed
+  // covariance values.
+  CircularBuffer render_power_;
+  CircularBuffer render_power_mean_;
+  CircularBuffer render_power_sigma_;

[hlundin-webrtc, 2016/10/14 08:00:39]

render_power_std_dev_

[ivoc, 2016/10/17 16:05:08]

Done.

+
+  MeanVarianceEstimator render_variance_;
+  MeanVarianceEstimator capture_variance_;
+  // Covariance estimates for different delay values.
+  std::vector<CovarianceEstimator> covariance_;
+  // Current echo likelihood.
+  float echo_likelihood_ = 0.f;
 };
 
 }  // namespace webrtc