New module for the adaptive level controlling functionality in the audio processing module

webrtc/modules/audio_processing/level_controller/peak_level_estimator.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/level_controller/peak_level_estimator.h"
+
+#include <algorithm>
+
+#include "webrtc/modules/audio_processing/audio_buffer.h"
+#include "webrtc/modules/audio_processing/logging/apm_data_dumper.h"
+
+namespace webrtc {
+
+PeakLevelEstimator::PeakLevelEstimator() {
+  Initialize();
+}
+
+PeakLevelEstimator::~PeakLevelEstimator() {}
+
+void PeakLevelEstimator::Initialize() {
+  peak_level_ = 1000.f;
+  hold_counter_ = 0;
+}
+
+float PeakLevelEstimator::Analyze(SignalClassifier::SignalType signal_type,
+                                  float frame_peak_level) {
+  if (frame_peak_level > 0) {
+    if (peak_level_ < frame_peak_level) {
+      // Smoothly update the estimate upwards when the frame peak level is
+      // higher than the estimate.
+      peak_level_ += 0.1f * (frame_peak_level - peak_level_);
+      hold_counter_ = 100;
+    } else {
+      hold_counter_ = std::max(0, hold_counter_ - 1);
+
+      // When the signal is highly non-stationary, update the estimate slowly
+      // downwards if the estimate is lower than the frame peak level.
+      if (signal_type == SignalClassifier::SignalType::kHighlyNonStationary &&
+          hold_counter_ == 0) {
+        peak_level_ =
+            std::max(peak_level_ + 0.01f * (frame_peak_level - peak_level_),
+                     peak_level_ * 0.995f);
+      }
+    }
+  }
+
+  peak_level_ = std::max(peak_level_, 30.f);
+
+  return peak_level_;
+}
+
+}  // namespace webrtc