Add a reliability term to the echo detector.

webrtc/modules/audio_processing/residual_echo_detector.cc

 /*
  *  Copyright (c) 2016 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/residual_echo_detector.h"
 
 #include <algorithm>
 #include <numeric>
 
 #include "webrtc/modules/audio_processing/audio_buffer.h"
 #include "webrtc/system_wrappers/include/metrics.h"
 
 namespace {
 
 float Power(rtc::ArrayView<const float> input) {
   return std::inner_product(input.begin(), input.end(), input.begin(), 0.f);
 }
 
 constexpr size_t kLookbackFrames = 650;
 // TODO(ivoc): Verify the size of this buffer.
 constexpr size_t kRenderBufferSize = 30;
+constexpr float kAlpha = 0.001f;
 
 }  // namespace
 
 namespace webrtc {
 
 ResidualEchoDetector::ResidualEchoDetector()
     : render_buffer_(kRenderBufferSize),
       render_power_(kLookbackFrames),
       render_power_mean_(kLookbackFrames),
       render_power_std_dev_(kLookbackFrames),
@@ skipping 55 matching lines @@
     const size_t read_index =
         (kLookbackFrames + next_insertion_index_ - delay) % kLookbackFrames;
     RTC_DCHECK_LT(read_index, render_power_.size());
     covariances_[delay].Update(capture_power, capture_mean,
                                capture_std_deviation, render_power_[read_index],
                                render_power_mean_[read_index],
                                render_power_std_dev_[read_index]);
     echo_likelihood_ = std::max(
         echo_likelihood_, covariances_[delay].normalized_cross_correlation());
   }
+  reliability_ = (1.0f - kAlpha) * reliability_ + kAlpha * 1.0f;

[hlundin-webrtc, 2016/11/16 09:46:30]

How long until this converges to close enough to 1.0? I'm wondering if it might
make sense to enclose those two lines in 
if (reliability_ < 1.0 - some_epsilon) {
  ...
}

[ivoc, 2016/11/16 12:30:38]

After about a minute the reliability is at 0.9975 (16 seconds to 0.8). I'm not
sure if a branch would be more or less efficient than 5 floating point
operations though.

[hlundin-webrtc, 2016/11/17 08:14:45]

Neither am I...

+  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 */);
 
   // Update the next insertion index.
   ++next_insertion_index_;
   next_insertion_index_ %= kLookbackFrames;
 }
 
 void ResidualEchoDetector::Initialize() {
@@ skipping 16 matching lines @@
   RTC_DCHECK_GE(160u, audio->num_frames_per_band());
 
   packed_buffer->clear();
   packed_buffer->insert(packed_buffer->end(),
                         audio->split_bands_const_f(0)[kBand0To8kHz],
                         (audio->split_bands_const_f(0)[kBand0To8kHz] +
                          audio->num_frames_per_band()));
 }
 
 }  // namespace webrtc