Revert "Deprecate the adaptive level controller"

This reverts commit 6f37ed78d99daa36e964ff0a65b205f0916d9949.

Reason for revert: <INSERT REASONING HERE>

Original change's description:
> Deprecate the adaptive level controller
> 
> Level control handled by default-on AGC.
> 
> Bug: none
> Change-Id: I405daeceece12c896d41156b649fcfd556726f77
> Reviewed-on: https://webrtc-review.googlesource.com/59682
> Reviewed-by: Fredrik Solenberg <solenberg@webrtc.org>
> Reviewed-by: Alex Loiko <aleloi@webrtc.org>
> Commit-Queue: Sam Zackrisson <saza@webrtc.org>
> Cr-Commit-Position: refs/heads/master@{#22305}

TBR=solenberg@webrtc.org,saza@webrtc.org,aleloi@webrtc.org

Change-Id: Ic52f41fcbebfd2291a51b17ac788313e1ceef163
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: none
Reviewed-on: https://webrtc-review.googlesource.com/60240
Reviewed-by: Sam Zackrisson <saza@webrtc.org>
Commit-Queue: Sam Zackrisson <saza@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#22308}
diff --git a/modules/audio_processing/BUILD.gn b/modules/audio_processing/BUILD.gn
index 93d3ec6..3dcea89 100644
--- a/modules/audio_processing/BUILD.gn
+++ b/modules/audio_processing/BUILD.gn
@@ -79,6 +79,27 @@
     "include/audio_processing.h",
     "include/config.cc",
     "include/config.h",
+    "level_controller/biquad_filter.cc",
+    "level_controller/biquad_filter.h",
+    "level_controller/down_sampler.cc",
+    "level_controller/down_sampler.h",
+    "level_controller/gain_applier.cc",
+    "level_controller/gain_applier.h",
+    "level_controller/gain_selector.cc",
+    "level_controller/gain_selector.h",
+    "level_controller/level_controller.cc",
+    "level_controller/level_controller.h",
+    "level_controller/level_controller_constants.h",
+    "level_controller/noise_level_estimator.cc",
+    "level_controller/noise_level_estimator.h",
+    "level_controller/noise_spectrum_estimator.cc",
+    "level_controller/noise_spectrum_estimator.h",
+    "level_controller/peak_level_estimator.cc",
+    "level_controller/peak_level_estimator.h",
+    "level_controller/saturating_gain_estimator.cc",
+    "level_controller/saturating_gain_estimator.h",
+    "level_controller/signal_classifier.cc",
+    "level_controller/signal_classifier.h",
     "level_estimator_impl.cc",
     "level_estimator_impl.h",
     "low_cut_filter.cc",
@@ -589,6 +610,7 @@
         "echo_detector/moving_max_unittest.cc",
         "echo_detector/normalized_covariance_estimator_unittest.cc",
         "gain_control_unittest.cc",
+        "level_controller/level_controller_unittest.cc",
         "level_estimator_unittest.cc",
         "low_cut_filter_unittest.cc",
         "noise_suppression_unittest.cc",
@@ -616,6 +638,7 @@
 
     sources = [
       "audio_processing_performance_unittest.cc",
+      "level_controller/level_controller_complexity_unittest.cc",
     ]
     deps = [
       ":audio_processing",
diff --git a/modules/audio_processing/audio_processing_impl.cc b/modules/audio_processing/audio_processing_impl.cc
index 0caa142..f4b8dee 100644
--- a/modules/audio_processing/audio_processing_impl.cc
+++ b/modules/audio_processing/audio_processing_impl.cc
@@ -37,6 +37,7 @@
 #if WEBRTC_INTELLIGIBILITY_ENHANCER
 #include "modules/audio_processing/intelligibility/intelligibility_enhancer.h"
 #endif
+#include "modules/audio_processing/level_controller/level_controller.h"
 #include "modules/audio_processing/level_estimator_impl.h"
 #include "modules/audio_processing/low_cut_filter.h"
 #include "modules/audio_processing/noise_suppression_impl.h"
@@ -187,6 +188,7 @@
     bool beamformer_enabled,
     bool adaptive_gain_controller_enabled,
     bool gain_controller2_enabled,
+    bool level_controller_enabled,
     bool echo_controller_enabled,
     bool voice_activity_detector_enabled,
     bool level_estimator_enabled,
@@ -206,6 +208,7 @@
       (adaptive_gain_controller_enabled != adaptive_gain_controller_enabled_);
   changed |=
       (gain_controller2_enabled != gain_controller2_enabled_);
+  changed |= (level_controller_enabled != level_controller_enabled_);
   changed |= (echo_controller_enabled != echo_controller_enabled_);
   changed |= (level_estimator_enabled != level_estimator_enabled_);
   changed |=
@@ -221,6 +224,7 @@
     beamformer_enabled_ = beamformer_enabled;
     adaptive_gain_controller_enabled_ = adaptive_gain_controller_enabled;
     gain_controller2_enabled_ = gain_controller2_enabled;
+    level_controller_enabled_ = level_controller_enabled;
     echo_controller_enabled_ = echo_controller_enabled;
     level_estimator_enabled_ = level_estimator_enabled;
     voice_activity_detector_enabled_ = voice_activity_detector_enabled;
@@ -252,7 +256,8 @@
 
 bool AudioProcessingImpl::ApmSubmoduleStates::CaptureFullBandProcessingActive()
     const {
-  return gain_controller2_enabled_ || capture_post_processor_enabled_;
+  return level_controller_enabled_ || gain_controller2_enabled_ ||
+         capture_post_processor_enabled_;
 }
 
 bool AudioProcessingImpl::ApmSubmoduleStates::RenderMultiBandSubModulesActive()
@@ -309,6 +314,7 @@
   std::unique_ptr<AgcManagerDirect> agc_manager;
   std::unique_ptr<GainController2> gain_controller2;
   std::unique_ptr<LowCutFilter> low_cut_filter;
+  std::unique_ptr<LevelController> level_controller;
   std::unique_ptr<EchoDetector> echo_detector;
   std::unique_ptr<EchoControl> echo_controller;
   std::unique_ptr<CustomProcessing> capture_post_processor;
@@ -434,6 +440,10 @@
       private_submodules_->echo_detector.reset(new ResidualEchoDetector());
     }
 
+    // TODO(peah): Move this creation to happen only when the level controller
+    // is enabled.
+    private_submodules_->level_controller.reset(new LevelController());
+
     // TODO(alessiob): Move the injected gain controller once injection is
     // implemented.
     private_submodules_->gain_controller2.reset(new GainController2());
@@ -592,6 +602,7 @@
                                                     proc_sample_rate_hz());
   public_submodules_->voice_detection->Initialize(proc_split_sample_rate_hz());
   public_submodules_->level_estimator->Initialize();
+  InitializeLevelController();
   InitializeResidualEchoDetector();
   InitializeEchoController();
   InitializeGainController2();
@@ -695,16 +706,40 @@
 void AudioProcessingImpl::ApplyConfig(const AudioProcessing::Config& config) {
   config_ = config;
 
+  bool config_ok = LevelController::Validate(config_.level_controller);
+  if (!config_ok) {
+    RTC_LOG(LS_ERROR) << "AudioProcessing module config error\n"
+                         "level_controller: "
+                      << LevelController::ToString(config_.level_controller)
+                      << "\nReverting to default parameter set";
+    config_.level_controller = AudioProcessing::Config::LevelController();
+  }
+
   // Run in a single-threaded manner when applying the settings.
   rtc::CritScope cs_render(&crit_render_);
   rtc::CritScope cs_capture(&crit_capture_);
 
+  // TODO(peah): Replace the use of capture_nonlocked_.level_controller_enabled
+  // with the value in config_ everywhere in the code.
+  if (capture_nonlocked_.level_controller_enabled !=
+      config_.level_controller.enabled) {
+    capture_nonlocked_.level_controller_enabled =
+        config_.level_controller.enabled;
+    // TODO(peah): Remove the conditional initialization to always initialize
+    // the level controller regardless of whether it is enabled or not.
+    InitializeLevelController();
+  }
+  RTC_LOG(LS_INFO) << "Level controller activated: "
+                   << capture_nonlocked_.level_controller_enabled;
+
+  private_submodules_->level_controller->ApplyConfig(config_.level_controller);
+
   InitializeLowCutFilter();
 
   RTC_LOG(LS_INFO) << "Highpass filter activated: "
                    << config_.high_pass_filter.enabled;
 
-  const bool config_ok = GainController2::Validate(config_.gain_controller2);
+  config_ok = GainController2::Validate(config_.gain_controller2);
   if (!config_ok) {
     RTC_LOG(LS_ERROR) << "AudioProcessing module config error\n"
                          "Gain Controller 2: "
@@ -1224,11 +1259,13 @@
 #if WEBRTC_INTELLIGIBILITY_ENHANCER
   if (capture_nonlocked_.intelligibility_enabled) {
     RTC_DCHECK(public_submodules_->noise_suppression->is_enabled());
-    const int gain_db =
-        public_submodules_->gain_control->is_enabled()
-            ? public_submodules_->gain_control->compression_gain_db()
-            : 0;
-    const float gain = DbToRatio(gain_db);
+    int gain_db = public_submodules_->gain_control->is_enabled() ?
+                  public_submodules_->gain_control->compression_gain_db() :
+                  0;
+    float gain = DbToRatio(gain_db);
+    gain *= capture_nonlocked_.level_controller_enabled ?
+            private_submodules_->level_controller->GetLastGain() :
+            1.f;
     public_submodules_->intelligibility_enhancer->SetCaptureNoiseEstimate(
         public_submodules_->noise_suppression->NoiseEstimate(), gain);
   }
@@ -1298,6 +1335,10 @@
     private_submodules_->gain_controller2->Process(capture_buffer);
   }
 
+  if (capture_nonlocked_.level_controller_enabled) {
+    private_submodules_->level_controller->Process(capture_buffer);
+  }
+
   if (private_submodules_->capture_post_processor) {
     private_submodules_->capture_post_processor->Process(capture_buffer);
   }
@@ -1725,6 +1766,7 @@
       capture_nonlocked_.beamformer_enabled,
       public_submodules_->gain_control->is_enabled(),
       config_.gain_controller2.enabled,
+      capture_nonlocked_.level_controller_enabled,
       capture_nonlocked_.echo_controller_enabled,
       public_submodules_->voice_detection->is_enabled(),
       public_submodules_->level_estimator->is_enabled(),
@@ -1790,6 +1832,10 @@
   }
 }
 
+void AudioProcessingImpl::InitializeLevelController() {
+  private_submodules_->level_controller->Initialize(proc_sample_rate_hz());
+}
+
 void AudioProcessingImpl::InitializeResidualEchoDetector() {
   RTC_DCHECK(private_submodules_->echo_detector);
   private_submodules_->echo_detector->Initialize(proc_sample_rate_hz(),
@@ -1892,6 +1938,9 @@
       public_submodules_->echo_cancellation->GetExperimentsDescription();
   // TODO(peah): Add semicolon-separated concatenations of experiment
   // descriptions for other submodules.
+  if (capture_nonlocked_.level_controller_enabled) {
+    experiments_description += "LevelController;";
+  }
   if (constants_.agc_clipped_level_min != kClippedLevelMin) {
     experiments_description += "AgcClippingLevelExperiment;";
   }
diff --git a/modules/audio_processing/audio_processing_impl.h b/modules/audio_processing/audio_processing_impl.h
index 55c47ac..e7c6621 100644
--- a/modules/audio_processing/audio_processing_impl.h
+++ b/modules/audio_processing/audio_processing_impl.h
@@ -169,6 +169,7 @@
                 bool beamformer_enabled,
                 bool adaptive_gain_controller_enabled,
                 bool gain_controller2_enabled,
+                bool level_controller_enabled,
                 bool echo_controller_enabled,
                 bool voice_activity_detector_enabled,
                 bool level_estimator_enabled,
@@ -192,6 +193,7 @@
     bool beamformer_enabled_ = false;
     bool adaptive_gain_controller_enabled_ = false;
     bool gain_controller2_enabled_ = false;
+    bool level_controller_enabled_ = false;
     bool echo_controller_enabled_ = false;
     bool level_estimator_enabled_ = false;
     bool voice_activity_detector_enabled_ = false;
@@ -231,6 +233,7 @@
       RTC_EXCLUSIVE_LOCKS_REQUIRED(crit_render_, crit_capture_);
   int InitializeLocked(const ProcessingConfig& config)
       RTC_EXCLUSIVE_LOCKS_REQUIRED(crit_render_, crit_capture_);
+  void InitializeLevelController() RTC_EXCLUSIVE_LOCKS_REQUIRED(crit_capture_);
   void InitializeResidualEchoDetector()
       RTC_EXCLUSIVE_LOCKS_REQUIRED(crit_render_, crit_capture_);
   void InitializeLowCutFilter() RTC_EXCLUSIVE_LOCKS_REQUIRED(crit_capture_);
@@ -383,6 +386,7 @@
     int stream_delay_ms;
     bool beamformer_enabled;
     bool intelligibility_enabled;
+    bool level_controller_enabled = false;
     bool echo_controller_enabled = false;
   } capture_nonlocked_;
 
diff --git a/modules/audio_processing/audio_processing_unittest.cc b/modules/audio_processing/audio_processing_unittest.cc
index 89d6cb9..ecaeed3 100644
--- a/modules/audio_processing/audio_processing_unittest.cc
+++ b/modules/audio_processing/audio_processing_unittest.cc
@@ -25,6 +25,7 @@
 #include "modules/audio_processing/common.h"
 #include "modules/audio_processing/include/audio_processing.h"
 #include "modules/audio_processing/include/mock_audio_processing.h"
+#include "modules/audio_processing/level_controller/level_controller_constants.h"
 #include "modules/audio_processing/test/protobuf_utils.h"
 #include "modules/audio_processing/test/test_utils.h"
 #include "modules/include/module_common_types.h"
@@ -2820,6 +2821,98 @@
 
 }  // namespace
 
+TEST(ApmConfiguration, DefaultBehavior) {
+  // Verify that the level controller is default off, it can be activated using
+  // the config, and that the default initial level is maintained after the
+  // config has been applied.
+  std::unique_ptr<AudioProcessingImpl> apm(
+      new rtc::RefCountedObject<AudioProcessingImpl>(webrtc::Config()));
+  AudioProcessing::Config config;
+  EXPECT_FALSE(apm->config_.level_controller.enabled);
+  // TODO(peah): Add test for the existence of the level controller object once
+  // that is created only when that is specified in the config.
+  // TODO(peah): Remove the testing for
+  // apm->capture_nonlocked_.level_controller_enabled once the value in config_
+  // is instead used to activate the level controller.
+  EXPECT_FALSE(apm->capture_nonlocked_.level_controller_enabled);
+  EXPECT_NEAR(kTargetLcPeakLeveldBFS,
+              apm->config_.level_controller.initial_peak_level_dbfs,
+              std::numeric_limits<float>::epsilon());
+  config.level_controller.enabled = true;
+  apm->ApplyConfig(config);
+  EXPECT_TRUE(apm->config_.level_controller.enabled);
+  // TODO(peah): Add test for the existence of the level controller object once
+  // that is created only when the that is specified in the config.
+  // TODO(peah): Remove the testing for
+  // apm->capture_nonlocked_.level_controller_enabled once the value in config_
+  // is instead used to activate the level controller.
+  EXPECT_TRUE(apm->capture_nonlocked_.level_controller_enabled);
+  EXPECT_NEAR(kTargetLcPeakLeveldBFS,
+              apm->config_.level_controller.initial_peak_level_dbfs,
+              std::numeric_limits<float>::epsilon());
+}
+
+TEST(ApmConfiguration, ValidConfigBehavior) {
+  // Verify that the initial level can be specified and is retained after the
+  // config has been applied.
+  std::unique_ptr<AudioProcessingImpl> apm(
+      new rtc::RefCountedObject<AudioProcessingImpl>(webrtc::Config()));
+  AudioProcessing::Config config;
+  config.level_controller.initial_peak_level_dbfs = -50.f;
+  apm->ApplyConfig(config);
+  EXPECT_FALSE(apm->config_.level_controller.enabled);
+  // TODO(peah): Add test for the existence of the level controller object once
+  // that is created only when the that is specified in the config.
+  // TODO(peah): Remove the testing for
+  // apm->capture_nonlocked_.level_controller_enabled once the value in config_
+  // is instead used to activate the level controller.
+  EXPECT_FALSE(apm->capture_nonlocked_.level_controller_enabled);
+  EXPECT_NEAR(-50.f, apm->config_.level_controller.initial_peak_level_dbfs,
+              std::numeric_limits<float>::epsilon());
+}
+
+TEST(ApmConfiguration, InValidConfigBehavior) {
+  // Verify that the config is properly reset when nonproper values are applied
+  // for the initial level.
+
+  // Verify that the config is properly reset when the specified initial peak
+  // level is too low.
+  std::unique_ptr<AudioProcessingImpl> apm(
+      new rtc::RefCountedObject<AudioProcessingImpl>(webrtc::Config()));
+  AudioProcessing::Config config;
+  config.level_controller.enabled = true;
+  config.level_controller.initial_peak_level_dbfs = -101.f;
+  apm->ApplyConfig(config);
+  EXPECT_FALSE(apm->config_.level_controller.enabled);
+  // TODO(peah): Add test for the existence of the level controller object once
+  // that is created only when the that is specified in the config.
+  // TODO(peah): Remove the testing for
+  // apm->capture_nonlocked_.level_controller_enabled once the value in config_
+  // is instead used to activate the level controller.
+  EXPECT_FALSE(apm->capture_nonlocked_.level_controller_enabled);
+  EXPECT_NEAR(kTargetLcPeakLeveldBFS,
+              apm->config_.level_controller.initial_peak_level_dbfs,
+              std::numeric_limits<float>::epsilon());
+
+  // Verify that the config is properly reset when the specified initial peak
+  // level is too high.
+  apm.reset(new rtc::RefCountedObject<AudioProcessingImpl>(webrtc::Config()));
+  config = AudioProcessing::Config();
+  config.level_controller.enabled = true;
+  config.level_controller.initial_peak_level_dbfs = 1.f;
+  apm->ApplyConfig(config);
+  EXPECT_FALSE(apm->config_.level_controller.enabled);
+  // TODO(peah): Add test for the existence of the level controller object once
+  // that is created only when that is specified in the config.
+  // TODO(peah): Remove the testing for
+  // apm->capture_nonlocked_.level_controller_enabled once the value in config_
+  // is instead used to activate the level controller.
+  EXPECT_FALSE(apm->capture_nonlocked_.level_controller_enabled);
+  EXPECT_NEAR(kTargetLcPeakLeveldBFS,
+              apm->config_.level_controller.initial_peak_level_dbfs,
+              std::numeric_limits<float>::epsilon());
+}
+
 TEST(ApmConfiguration, EnablePostProcessing) {
   // Verify that apm uses a capture post processing module if one is provided.
   webrtc::Config webrtc_config;
@@ -2914,6 +3007,7 @@
   config.residual_echo_detector.enabled = true;
   config.high_pass_filter.enabled = false;
   config.gain_controller2.enabled = false;
+  config.level_controller.enabled = false;
   apm->ApplyConfig(config);
   EXPECT_EQ(apm->gain_control()->Enable(false), 0);
   EXPECT_EQ(apm->level_estimator()->Enable(false), 0);
diff --git a/modules/audio_processing/include/audio_processing.h b/modules/audio_processing/include/audio_processing.h
index 33ecf89..7057f28 100644
--- a/modules/audio_processing/include/audio_processing.h
+++ b/modules/audio_processing/include/audio_processing.h
@@ -211,8 +211,8 @@
 // AudioProcessing* apm = AudioProcessingBuilder().Create();
 //
 // AudioProcessing::Config config;
+// config.level_controller.enabled = true;
 // config.high_pass_filter.enabled = true;
-// config.gain_controller2.enabled = true;
 // apm->ApplyConfig(config)
 //
 // apm->echo_cancellation()->enable_drift_compensation(false);
@@ -262,6 +262,14 @@
   // by changing the default values in the AudioProcessing::Config struct.
   // The config is applied by passing the struct to the ApplyConfig method.
   struct Config {
+    struct LevelController {
+      bool enabled = false;
+
+      // Sets the initial peak level to use inside the level controller in order
+      // to compute the signal gain. The unit for the peak level is dBFS and
+      // the allowed range is [-100, 0].
+      float initial_peak_level_dbfs = -6.0206f;
+    } level_controller;
     struct ResidualEchoDetector {
       bool enabled = true;
     } residual_echo_detector;
diff --git a/modules/audio_processing/include/config.h b/modules/audio_processing/include/config.h
index 7615f62..7c34de8 100644
--- a/modules/audio_processing/include/config.h
+++ b/modules/audio_processing/include/config.h
@@ -35,7 +35,7 @@
   kIntelligibility,
   kEchoCanceller3,  // Deprecated
   kAecRefinedAdaptiveFilter,
-  kLevelControl  // Deprecated
+  kLevelControl
 };
 
 // Class Config is designed to ease passing a set of options across webrtc code.
diff --git a/modules/audio_processing/level_controller/biquad_filter.cc b/modules/audio_processing/level_controller/biquad_filter.cc
new file mode 100644
index 0000000..5a4ddc8
--- /dev/null
+++ b/modules/audio_processing/level_controller/biquad_filter.cc
@@ -0,0 +1,35 @@
+/*
+ *  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 "modules/audio_processing/level_controller/biquad_filter.h"
+
+namespace webrtc {
+
+// This method applies a biquad filter to an input signal x to produce an
+// output signal y. The biquad coefficients are specified at the construction
+// of the object.
+void BiQuadFilter::Process(rtc::ArrayView<const float> x,
+                           rtc::ArrayView<float> y) {
+  for (size_t k = 0; k < x.size(); ++k) {
+    // Use temporary variable for x[k] to allow in-place function call
+    // (that x and y refer to the same array).
+    const float tmp = x[k];
+    y[k] = coefficients_.b[0] * tmp + coefficients_.b[1] * biquad_state_.b[0] +
+           coefficients_.b[2] * biquad_state_.b[1] -
+           coefficients_.a[0] * biquad_state_.a[0] -
+           coefficients_.a[1] * biquad_state_.a[1];
+    biquad_state_.b[1] = biquad_state_.b[0];
+    biquad_state_.b[0] = tmp;
+    biquad_state_.a[1] = biquad_state_.a[0];
+    biquad_state_.a[0] = y[k];
+  }
+}
+
+}  // namespace webrtc
diff --git a/modules/audio_processing/level_controller/biquad_filter.h b/modules/audio_processing/level_controller/biquad_filter.h
new file mode 100644
index 0000000..dad104d
--- /dev/null
+++ b/modules/audio_processing/level_controller/biquad_filter.h
@@ -0,0 +1,58 @@
+/*
+ *  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.
+ */
+
+#ifndef MODULES_AUDIO_PROCESSING_LEVEL_CONTROLLER_BIQUAD_FILTER_H_
+#define MODULES_AUDIO_PROCESSING_LEVEL_CONTROLLER_BIQUAD_FILTER_H_
+
+#include <vector>
+
+#include "api/array_view.h"
+#include "rtc_base/arraysize.h"
+#include "rtc_base/constructormagic.h"
+
+namespace webrtc {
+
+class BiQuadFilter {
+ public:
+  struct BiQuadCoefficients {
+    float b[3];
+    float a[2];
+  };
+
+  BiQuadFilter() = default;
+
+  void Initialize(const BiQuadCoefficients& coefficients) {
+    coefficients_ = coefficients;
+  }
+
+  // Produces a filtered output y of the input x. Both x and y need to
+  // have the same length.
+  void Process(rtc::ArrayView<const float> x, rtc::ArrayView<float> y);
+
+ private:
+  struct BiQuadState {
+    BiQuadState() {
+      std::fill(b, b + arraysize(b), 0.f);
+      std::fill(a, a + arraysize(a), 0.f);
+    }
+
+    float b[2];
+    float a[2];
+  };
+
+  BiQuadState biquad_state_;
+  BiQuadCoefficients coefficients_;
+
+  RTC_DISALLOW_COPY_AND_ASSIGN(BiQuadFilter);
+};
+
+}  // namespace webrtc
+
+#endif  // MODULES_AUDIO_PROCESSING_LEVEL_CONTROLLER_BIQUAD_FILTER_H_
diff --git a/modules/audio_processing/level_controller/down_sampler.cc b/modules/audio_processing/level_controller/down_sampler.cc
new file mode 100644
index 0000000..a1702f4
--- /dev/null
+++ b/modules/audio_processing/level_controller/down_sampler.cc
@@ -0,0 +1,100 @@
+/*
+ *  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 "modules/audio_processing/level_controller/down_sampler.h"
+
+#include <string.h>
+#include <algorithm>
+#include <vector>
+
+#include "modules/audio_processing/include/audio_processing.h"
+#include "modules/audio_processing/level_controller/biquad_filter.h"
+#include "modules/audio_processing/logging/apm_data_dumper.h"
+#include "rtc_base/checks.h"
+
+namespace webrtc {
+namespace {
+
+// Bandlimiter coefficients computed based on that only
+// the first 40 bins of the spectrum for the downsampled
+// signal are used.
+// [B,A] = butter(2,(41/64*4000)/8000)
+const BiQuadFilter::BiQuadCoefficients kLowPassFilterCoefficients_16kHz = {
+    {0.1455f, 0.2911f, 0.1455f},
+    {-0.6698f, 0.2520f}};
+
+// [B,A] = butter(2,(41/64*4000)/16000)
+const BiQuadFilter::BiQuadCoefficients kLowPassFilterCoefficients_32kHz = {
+    {0.0462f, 0.0924f, 0.0462f},
+    {-1.3066f, 0.4915f}};
+
+// [B,A] = butter(2,(41/64*4000)/24000)
+const BiQuadFilter::BiQuadCoefficients kLowPassFilterCoefficients_48kHz = {
+    {0.0226f, 0.0452f, 0.0226f},
+    {-1.5320f, 0.6224f}};
+
+}  // namespace
+
+DownSampler::DownSampler(ApmDataDumper* data_dumper)
+    : data_dumper_(data_dumper) {
+  Initialize(48000);
+}
+void DownSampler::Initialize(int sample_rate_hz) {
+  RTC_DCHECK(sample_rate_hz == AudioProcessing::kSampleRate8kHz ||
+             sample_rate_hz == AudioProcessing::kSampleRate16kHz ||
+             sample_rate_hz == AudioProcessing::kSampleRate32kHz ||
+             sample_rate_hz == AudioProcessing::kSampleRate48kHz);
+
+  sample_rate_hz_ = sample_rate_hz;
+  down_sampling_factor_ = rtc::CheckedDivExact(sample_rate_hz_, 8000);
+
+  /// Note that the down sampling filter is not used if the sample rate is 8
+  /// kHz.
+  if (sample_rate_hz_ == AudioProcessing::kSampleRate16kHz) {
+    low_pass_filter_.Initialize(kLowPassFilterCoefficients_16kHz);
+  } else if (sample_rate_hz_ == AudioProcessing::kSampleRate32kHz) {
+    low_pass_filter_.Initialize(kLowPassFilterCoefficients_32kHz);
+  } else if (sample_rate_hz_ == AudioProcessing::kSampleRate48kHz) {
+    low_pass_filter_.Initialize(kLowPassFilterCoefficients_48kHz);
+  }
+}
+
+void DownSampler::DownSample(rtc::ArrayView<const float> in,
+                             rtc::ArrayView<float> out) {
+  data_dumper_->DumpWav("lc_down_sampler_input", in, sample_rate_hz_, 1);
+  RTC_DCHECK_EQ(sample_rate_hz_ * AudioProcessing::kChunkSizeMs / 1000,
+                in.size());
+  RTC_DCHECK_EQ(
+      AudioProcessing::kSampleRate8kHz * AudioProcessing::kChunkSizeMs / 1000,
+      out.size());
+  const size_t kMaxNumFrames =
+      AudioProcessing::kSampleRate48kHz * AudioProcessing::kChunkSizeMs / 1000;
+  float x[kMaxNumFrames];
+
+  // Band-limit the signal to 4 kHz.
+  if (sample_rate_hz_ != AudioProcessing::kSampleRate8kHz) {
+    low_pass_filter_.Process(in, rtc::ArrayView<float>(x, in.size()));
+
+    // Downsample the signal.
+    size_t k = 0;
+    for (size_t j = 0; j < out.size(); ++j) {
+      RTC_DCHECK_GT(kMaxNumFrames, k);
+      out[j] = x[k];
+      k += down_sampling_factor_;
+    }
+  } else {
+    std::copy(in.data(), in.data() + in.size(), out.data());
+  }
+
+  data_dumper_->DumpWav("lc_down_sampler_output", out,
+                        AudioProcessing::kSampleRate8kHz, 1);
+}
+
+}  // namespace webrtc
diff --git a/modules/audio_processing/level_controller/down_sampler.h b/modules/audio_processing/level_controller/down_sampler.h
new file mode 100644
index 0000000..d650242
--- /dev/null
+++ b/modules/audio_processing/level_controller/down_sampler.h
@@ -0,0 +1,40 @@
+/*
+ *  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.
+ */
+
+#ifndef MODULES_AUDIO_PROCESSING_LEVEL_CONTROLLER_DOWN_SAMPLER_H_
+#define MODULES_AUDIO_PROCESSING_LEVEL_CONTROLLER_DOWN_SAMPLER_H_
+
+#include "api/array_view.h"
+#include "modules/audio_processing/level_controller/biquad_filter.h"
+#include "rtc_base/constructormagic.h"
+
+namespace webrtc {
+
+class ApmDataDumper;
+
+class DownSampler {
+ public:
+  explicit DownSampler(ApmDataDumper* data_dumper);
+  void Initialize(int sample_rate_hz);
+
+  void DownSample(rtc::ArrayView<const float> in, rtc::ArrayView<float> out);
+
+ private:
+  ApmDataDumper* data_dumper_;
+  int sample_rate_hz_;
+  int down_sampling_factor_;
+  BiQuadFilter low_pass_filter_;
+
+  RTC_DISALLOW_IMPLICIT_CONSTRUCTORS(DownSampler);
+};
+
+}  // namespace webrtc
+
+#endif  // MODULES_AUDIO_PROCESSING_LEVEL_CONTROLLER_DOWN_SAMPLER_H_
diff --git a/modules/audio_processing/level_controller/gain_applier.cc b/modules/audio_processing/level_controller/gain_applier.cc
new file mode 100644
index 0000000..018f809
--- /dev/null
+++ b/modules/audio_processing/level_controller/gain_applier.cc
@@ -0,0 +1,160 @@
+/*
+ *  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 "modules/audio_processing/level_controller/gain_applier.h"
+
+#include <algorithm>
+
+#include "api/array_view.h"
+#include "rtc_base/checks.h"
+
+#include "modules/audio_processing/audio_buffer.h"
+#include "modules/audio_processing/logging/apm_data_dumper.h"
+
+namespace webrtc {
+namespace {
+
+const float kMaxSampleValue = 32767.f;
+const float kMinSampleValue = -32767.f;
+
+int CountSaturations(rtc::ArrayView<const float> in) {
+  return std::count_if(in.begin(), in.end(), [](const float& v) {
+    return v >= kMaxSampleValue || v <= kMinSampleValue;
+  });
+}
+
+int CountSaturations(const AudioBuffer& audio) {
+  int num_saturations = 0;
+  for (size_t k = 0; k < audio.num_channels(); ++k) {
+    num_saturations += CountSaturations(rtc::ArrayView<const float>(
+        audio.channels_const_f()[k], audio.num_frames()));
+  }
+  return num_saturations;
+}
+
+void LimitToAllowedRange(rtc::ArrayView<float> x) {
+  for (auto& v : x) {
+    v = std::max(kMinSampleValue, v);
+    v = std::min(kMaxSampleValue, v);
+  }
+}
+
+void LimitToAllowedRange(AudioBuffer* audio) {
+  for (size_t k = 0; k < audio->num_channels(); ++k) {
+    LimitToAllowedRange(
+        rtc::ArrayView<float>(audio->channels_f()[k], audio->num_frames()));
+  }
+}
+
+float ApplyIncreasingGain(float new_gain,
+                          float old_gain,
+                          float step_size,
+                          rtc::ArrayView<float> x) {
+  RTC_DCHECK_LT(0.f, step_size);
+  float gain = old_gain;
+  for (auto& v : x) {
+    gain = std::min(new_gain, gain + step_size);
+    v *= gain;
+  }
+  return gain;
+}
+
+float ApplyDecreasingGain(float new_gain,
+                          float old_gain,
+                          float step_size,
+                          rtc::ArrayView<float> x) {
+  RTC_DCHECK_GT(0.f, step_size);
+  float gain = old_gain;
+  for (auto& v : x) {
+    gain = std::max(new_gain, gain + step_size);
+    v *= gain;
+  }
+  return gain;
+}
+
+float ApplyConstantGain(float gain, rtc::ArrayView<float> x) {
+  for (auto& v : x) {
+    v *= gain;
+  }
+
+  return gain;
+}
+
+float ApplyGain(float new_gain,
+                float old_gain,
+                float increase_step_size,
+                float decrease_step_size,
+                rtc::ArrayView<float> x) {
+  RTC_DCHECK_LT(0.f, increase_step_size);
+  RTC_DCHECK_GT(0.f, decrease_step_size);
+  if (new_gain == old_gain) {
+    return ApplyConstantGain(new_gain, x);
+  } else if (new_gain > old_gain) {
+    return ApplyIncreasingGain(new_gain, old_gain, increase_step_size, x);
+  } else {
+    return ApplyDecreasingGain(new_gain, old_gain, decrease_step_size, x);
+  }
+}
+
+}  // namespace
+
+GainApplier::GainApplier(ApmDataDumper* data_dumper)
+    : data_dumper_(data_dumper) {}
+
+void GainApplier::Initialize(int sample_rate_hz) {
+  RTC_DCHECK(sample_rate_hz == AudioProcessing::kSampleRate8kHz ||
+             sample_rate_hz == AudioProcessing::kSampleRate16kHz ||
+             sample_rate_hz == AudioProcessing::kSampleRate32kHz ||
+             sample_rate_hz == AudioProcessing::kSampleRate48kHz);
+  const float kGainIncreaseStepSize48kHz = 0.0001f;
+  const float kGainDecreaseStepSize48kHz = -0.01f;
+  const float kGainSaturatedDecreaseStepSize48kHz = -0.05f;
+
+  last_frame_was_saturated_ = false;
+  old_gain_ = 1.f;
+  gain_increase_step_size_ =
+      kGainIncreaseStepSize48kHz *
+      (static_cast<float>(AudioProcessing::kSampleRate48kHz) / sample_rate_hz);
+  gain_normal_decrease_step_size_ =
+      kGainDecreaseStepSize48kHz *
+      (static_cast<float>(AudioProcessing::kSampleRate48kHz) / sample_rate_hz);
+  gain_saturated_decrease_step_size_ =
+      kGainSaturatedDecreaseStepSize48kHz *
+      (static_cast<float>(AudioProcessing::kSampleRate48kHz) / sample_rate_hz);
+}
+
+int GainApplier::Process(float new_gain, AudioBuffer* audio) {
+  RTC_CHECK_NE(0.f, gain_increase_step_size_);
+  RTC_CHECK_NE(0.f, gain_normal_decrease_step_size_);
+  RTC_CHECK_NE(0.f, gain_saturated_decrease_step_size_);
+  int num_saturations = 0;
+  if (new_gain != 1.f) {
+    float last_applied_gain = 1.f;
+    float gain_decrease_step_size = last_frame_was_saturated_
+                                        ? gain_saturated_decrease_step_size_
+                                        : gain_normal_decrease_step_size_;
+    for (size_t k = 0; k < audio->num_channels(); ++k) {
+      last_applied_gain = ApplyGain(
+          new_gain, old_gain_, gain_increase_step_size_,
+          gain_decrease_step_size,
+          rtc::ArrayView<float>(audio->channels_f()[k], audio->num_frames()));
+    }
+
+    num_saturations = CountSaturations(*audio);
+    LimitToAllowedRange(audio);
+    old_gain_ = last_applied_gain;
+  }
+
+  data_dumper_->DumpRaw("lc_last_applied_gain", 1, &old_gain_);
+
+  return num_saturations;
+}
+
+}  // namespace webrtc
diff --git a/modules/audio_processing/level_controller/gain_applier.h b/modules/audio_processing/level_controller/gain_applier.h
new file mode 100644
index 0000000..5669f45
--- /dev/null
+++ b/modules/audio_processing/level_controller/gain_applier.h
@@ -0,0 +1,42 @@
+/*
+ *  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.
+ */
+
+#ifndef MODULES_AUDIO_PROCESSING_LEVEL_CONTROLLER_GAIN_APPLIER_H_
+#define MODULES_AUDIO_PROCESSING_LEVEL_CONTROLLER_GAIN_APPLIER_H_
+
+#include "rtc_base/constructormagic.h"
+
+namespace webrtc {
+
+class ApmDataDumper;
+class AudioBuffer;
+
+class GainApplier {
+ public:
+  explicit GainApplier(ApmDataDumper* data_dumper);
+  void Initialize(int sample_rate_hz);
+
+  // Applies the specified gain to the audio frame and returns the resulting
+  // number of saturated sample values.
+  int Process(float new_gain, AudioBuffer* audio);
+
+ private:
+  ApmDataDumper* const data_dumper_;
+  float old_gain_ = 1.f;
+  float gain_increase_step_size_ = 0.f;
+  float gain_normal_decrease_step_size_ = 0.f;
+  float gain_saturated_decrease_step_size_ = 0.f;
+  bool last_frame_was_saturated_;
+  RTC_DISALLOW_IMPLICIT_CONSTRUCTORS(GainApplier);
+};
+
+}  // namespace webrtc
+
+#endif  // MODULES_AUDIO_PROCESSING_LEVEL_CONTROLLER_GAIN_APPLIER_H_
diff --git a/modules/audio_processing/level_controller/gain_selector.cc b/modules/audio_processing/level_controller/gain_selector.cc
new file mode 100644
index 0000000..3ab75b1
--- /dev/null
+++ b/modules/audio_processing/level_controller/gain_selector.cc
@@ -0,0 +1,87 @@
+/*
+ *  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 "modules/audio_processing/level_controller/gain_selector.h"
+
+#include <math.h>
+#include <algorithm>
+
+#include "modules/audio_processing/include/audio_processing.h"
+#include "modules/audio_processing/level_controller/level_controller_constants.h"
+#include "rtc_base/checks.h"
+
+namespace webrtc {
+
+GainSelector::GainSelector() {
+  Initialize(AudioProcessing::kSampleRate48kHz);
+}
+
+void GainSelector::Initialize(int sample_rate_hz) {
+  gain_ = 1.f;
+  frame_length_ = rtc::CheckedDivExact(sample_rate_hz, 100);
+  highly_nonstationary_signal_hold_counter_ = 0;
+}
+
+// Chooses the gain to apply by the level controller such that
+// 1) The level of the stationary noise does not exceed
+//    a predefined threshold.
+// 2) The gain does not exceed the gain that has been found
+//    to saturate the signal.
+// 3) The peak level achieves the target peak level.
+// 4) The gain is not below 1.
+// 4) The gain is 1 if the signal has been classified as stationary
+//    for a long time.
+// 5) The gain is not above the maximum gain.
+float GainSelector::GetNewGain(float peak_level,
+                               float noise_energy,
+                               float saturating_gain,
+                               bool gain_jumpstart,
+                               SignalClassifier::SignalType signal_type) {
+  RTC_DCHECK_LT(0.f, peak_level);
+
+  if (signal_type == SignalClassifier::SignalType::kHighlyNonStationary ||
+      gain_jumpstart) {
+    highly_nonstationary_signal_hold_counter_ = 100;
+  } else {
+    highly_nonstationary_signal_hold_counter_ =
+        std::max(0, highly_nonstationary_signal_hold_counter_ - 1);
+  }
+
+  float desired_gain;
+  if (highly_nonstationary_signal_hold_counter_ > 0) {
+    // Compute a desired gain that ensures that the peak level is amplified to
+    // the target level.
+    desired_gain = kTargetLcPeakLevel / peak_level;
+
+    // Limit the desired gain so that it does not amplify the noise too much.
+    float max_noise_energy = kMaxLcNoisePower * frame_length_;
+    if (noise_energy * desired_gain * desired_gain > max_noise_energy) {
+      RTC_DCHECK_LE(0.f, noise_energy);
+      desired_gain = sqrtf(max_noise_energy / noise_energy);
+    }
+  } else {
+    // If the signal has been stationary for a long while, apply a gain of 1 to
+    // avoid amplifying pure noise.
+    desired_gain = 1.0f;
+  }
+
+  // Smootly update the gain towards the desired gain.
+  gain_ += 0.2f * (desired_gain - gain_);
+
+  // Limit the gain to not exceed the maximum and the saturating gains, and to
+  // ensure that the lowest possible gain is 1.
+  gain_ = std::min(gain_, saturating_gain);
+  gain_ = std::min(gain_, kMaxLcGain);
+  gain_ = std::max(gain_, 1.f);
+
+  return gain_;
+}
+
+}  // namespace webrtc
diff --git a/modules/audio_processing/level_controller/gain_selector.h b/modules/audio_processing/level_controller/gain_selector.h
new file mode 100644
index 0000000..7966c43
--- /dev/null
+++ b/modules/audio_processing/level_controller/gain_selector.h
@@ -0,0 +1,40 @@
+/*
+ *  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.
+ */
+
+#ifndef MODULES_AUDIO_PROCESSING_LEVEL_CONTROLLER_GAIN_SELECTOR_H_
+#define MODULES_AUDIO_PROCESSING_LEVEL_CONTROLLER_GAIN_SELECTOR_H_
+
+#include "rtc_base/constructormagic.h"
+
+#include "modules/audio_processing/level_controller/signal_classifier.h"
+
+namespace webrtc {
+
+class GainSelector {
+ public:
+  GainSelector();
+  void Initialize(int sample_rate_hz);
+  float GetNewGain(float peak_level,
+                   float noise_energy,
+                   float saturating_gain,
+                   bool gain_jumpstart,
+                   SignalClassifier::SignalType signal_type);
+
+ private:
+  float gain_;
+  size_t frame_length_;
+  int highly_nonstationary_signal_hold_counter_;
+
+  RTC_DISALLOW_COPY_AND_ASSIGN(GainSelector);
+};
+
+}  // namespace webrtc
+
+#endif  // MODULES_AUDIO_PROCESSING_LEVEL_CONTROLLER_GAIN_SELECTOR_H_
diff --git a/modules/audio_processing/level_controller/level_controller.cc b/modules/audio_processing/level_controller/level_controller.cc
new file mode 100644
index 0000000..b7854a0
--- /dev/null
+++ b/modules/audio_processing/level_controller/level_controller.cc
@@ -0,0 +1,295 @@
+/*
+ *  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 "modules/audio_processing/level_controller/level_controller.h"
+
+#include <math.h>
+#include <algorithm>
+#include <numeric>
+
+#include "api/array_view.h"
+#include "modules/audio_processing/audio_buffer.h"
+#include "modules/audio_processing/level_controller/gain_applier.h"
+#include "modules/audio_processing/level_controller/gain_selector.h"
+#include "modules/audio_processing/level_controller/noise_level_estimator.h"
+#include "modules/audio_processing/level_controller/peak_level_estimator.h"
+#include "modules/audio_processing/level_controller/saturating_gain_estimator.h"
+#include "modules/audio_processing/level_controller/signal_classifier.h"
+#include "modules/audio_processing/logging/apm_data_dumper.h"
+#include "rtc_base/arraysize.h"
+#include "rtc_base/checks.h"
+#include "rtc_base/logging.h"
+#include "system_wrappers/include/metrics.h"
+
+namespace webrtc {
+namespace {
+
+void UpdateAndRemoveDcLevel(float forgetting_factor,
+                            float* dc_level,
+                            rtc::ArrayView<float> x) {
+  RTC_DCHECK(!x.empty());
+  float mean =
+      std::accumulate(x.begin(), x.end(), 0.0f) / static_cast<float>(x.size());
+  *dc_level += forgetting_factor * (mean - *dc_level);
+
+  for (float& v : x) {
+    v -= *dc_level;
+  }
+}
+
+float FrameEnergy(const AudioBuffer& audio) {
+  float energy = 0.f;
+  for (size_t k = 0; k < audio.num_channels(); ++k) {
+    float channel_energy =
+        std::accumulate(audio.channels_const_f()[k],
+                        audio.channels_const_f()[k] + audio.num_frames(), 0.f,
+                        [](float a, float b) -> float { return a + b * b; });
+    energy = std::max(channel_energy, energy);
+  }
+  return energy;
+}
+
+float PeakLevel(const AudioBuffer& audio) {
+  float peak_level = 0.f;
+  for (size_t k = 0; k < audio.num_channels(); ++k) {
+    auto* channel_peak_level = std::max_element(
+        audio.channels_const_f()[k],
+        audio.channels_const_f()[k] + audio.num_frames(),
+        [](float a, float b) { return std::abs(a) < std::abs(b); });
+    peak_level = std::max(*channel_peak_level, peak_level);
+  }
+  return peak_level;
+}
+
+const int kMetricsFrameInterval = 1000;
+
+}  // namespace
+
+int LevelController::instance_count_ = 0;
+
+void LevelController::Metrics::Initialize(int sample_rate_hz) {
+  RTC_DCHECK(sample_rate_hz == AudioProcessing::kSampleRate8kHz ||
+             sample_rate_hz == AudioProcessing::kSampleRate16kHz ||
+             sample_rate_hz == AudioProcessing::kSampleRate32kHz ||
+             sample_rate_hz == AudioProcessing::kSampleRate48kHz);
+
+  Reset();
+  frame_length_ = rtc::CheckedDivExact(sample_rate_hz, 100);
+}
+
+void LevelController::Metrics::Reset() {
+  metrics_frame_counter_ = 0;
+  gain_sum_ = 0.f;
+  peak_level_sum_ = 0.f;
+  noise_energy_sum_ = 0.f;
+  max_gain_ = 0.f;
+  max_peak_level_ = 0.f;
+  max_noise_energy_ = 0.f;
+}
+
+void LevelController::Metrics::Update(float long_term_peak_level,
+                                      float noise_energy,
+                                      float gain,
+                                      float frame_peak_level) {
+  const float kdBFSOffset = 90.3090f;
+  gain_sum_ += gain;
+  peak_level_sum_ += long_term_peak_level;
+  noise_energy_sum_ += noise_energy;
+  max_gain_ = std::max(max_gain_, gain);
+  max_peak_level_ = std::max(max_peak_level_, long_term_peak_level);
+  max_noise_energy_ = std::max(max_noise_energy_, noise_energy);
+
+  ++metrics_frame_counter_;
+  if (metrics_frame_counter_ == kMetricsFrameInterval) {
+    RTC_DCHECK_LT(0, frame_length_);
+    RTC_DCHECK_LT(0, kMetricsFrameInterval);
+
+    const int max_noise_power_dbfs = static_cast<int>(
+        10 * log10(max_noise_energy_ / frame_length_ + 1e-10f) - kdBFSOffset);
+    RTC_HISTOGRAM_COUNTS("WebRTC.Audio.LevelControl.MaxNoisePower",
+                         max_noise_power_dbfs, -90, 0, 50);
+
+    const int average_noise_power_dbfs = static_cast<int>(
+        10 * log10(noise_energy_sum_ / (frame_length_ * kMetricsFrameInterval) +
+                   1e-10f) -
+        kdBFSOffset);
+    RTC_HISTOGRAM_COUNTS("WebRTC.Audio.LevelControl.AverageNoisePower",
+                         average_noise_power_dbfs, -90, 0, 50);
+
+    const int max_peak_level_dbfs = static_cast<int>(
+        10 * log10(max_peak_level_ * max_peak_level_ + 1e-10f) - kdBFSOffset);
+    RTC_HISTOGRAM_COUNTS("WebRTC.Audio.LevelControl.MaxPeakLevel",
+                         max_peak_level_dbfs, -90, 0, 50);
+
+    const int average_peak_level_dbfs = static_cast<int>(
+        10 * log10(peak_level_sum_ * peak_level_sum_ /
+                       (kMetricsFrameInterval * kMetricsFrameInterval) +
+                   1e-10f) -
+        kdBFSOffset);
+    RTC_HISTOGRAM_COUNTS("WebRTC.Audio.LevelControl.AveragePeakLevel",
+                         average_peak_level_dbfs, -90, 0, 50);
+
+    RTC_DCHECK_LE(1.f, max_gain_);
+    RTC_DCHECK_LE(1.f, gain_sum_ / kMetricsFrameInterval);
+
+    const int max_gain_db = static_cast<int>(10 * log10(max_gain_ * max_gain_));
+    RTC_HISTOGRAM_COUNTS("WebRTC.Audio.LevelControl.MaxGain", max_gain_db, 0,
+                         33, 30);
+
+    const int average_gain_db = static_cast<int>(
+        10 * log10(gain_sum_ * gain_sum_ /
+                   (kMetricsFrameInterval * kMetricsFrameInterval)));
+    RTC_HISTOGRAM_COUNTS("WebRTC.Audio.LevelControl.AverageGain",
+                         average_gain_db, 0, 33, 30);
+
+    const int long_term_peak_level_dbfs = static_cast<int>(
+        10 * log10(long_term_peak_level * long_term_peak_level + 1e-10f) -
+        kdBFSOffset);
+
+    const int frame_peak_level_dbfs = static_cast<int>(
+        10 * log10(frame_peak_level * frame_peak_level + 1e-10f) - kdBFSOffset);
+
+    RTC_LOG(LS_INFO) << "Level Controller metrics: {Max noise power: "
+                     << max_noise_power_dbfs
+                     << " dBFS, Average noise power: "
+                     << average_noise_power_dbfs
+                     << " dBFS, Max long term peak level: "
+                     << max_peak_level_dbfs
+                     << " dBFS, Average long term peak level: "
+                     << average_peak_level_dbfs
+                     << " dBFS, Max gain: "
+                     << max_gain_db
+                     << " dB, Average gain: "
+                     << average_gain_db
+                     << " dB, Long term peak level: "
+                     << long_term_peak_level_dbfs
+                     << " dBFS, Last frame peak level: "
+                     << frame_peak_level_dbfs
+                     << " dBFS}";
+
+    Reset();
+  }
+}
+
+LevelController::LevelController()
+    : data_dumper_(new ApmDataDumper(instance_count_)),
+      gain_applier_(data_dumper_.get()),
+      signal_classifier_(data_dumper_.get()),
+      peak_level_estimator_(kTargetLcPeakLeveldBFS) {
+  Initialize(AudioProcessing::kSampleRate48kHz);
+  ++instance_count_;
+}
+
+LevelController::~LevelController() {}
+
+void LevelController::Initialize(int sample_rate_hz) {
+  RTC_DCHECK(sample_rate_hz == AudioProcessing::kSampleRate8kHz ||
+             sample_rate_hz == AudioProcessing::kSampleRate16kHz ||
+             sample_rate_hz == AudioProcessing::kSampleRate32kHz ||
+             sample_rate_hz == AudioProcessing::kSampleRate48kHz);
+  data_dumper_->InitiateNewSetOfRecordings();
+  gain_selector_.Initialize(sample_rate_hz);
+  gain_applier_.Initialize(sample_rate_hz);
+  signal_classifier_.Initialize(sample_rate_hz);
+  noise_level_estimator_.Initialize(sample_rate_hz);
+  peak_level_estimator_.Initialize(config_.initial_peak_level_dbfs);
+  saturating_gain_estimator_.Initialize();
+  metrics_.Initialize(sample_rate_hz);
+
+  last_gain_ = 1.0f;
+  sample_rate_hz_ = sample_rate_hz;
+  dc_forgetting_factor_ = 0.01f * sample_rate_hz / 48000.f;
+  std::fill(dc_level_, dc_level_ + arraysize(dc_level_), 0.f);
+}
+
+void LevelController::Process(AudioBuffer* audio) {
+  RTC_DCHECK_LT(0, audio->num_channels());
+  RTC_DCHECK_GE(2, audio->num_channels());
+  RTC_DCHECK_NE(0.f, dc_forgetting_factor_);
+  RTC_DCHECK(sample_rate_hz_);
+  data_dumper_->DumpWav("lc_input", audio->num_frames(),
+                        audio->channels_const_f()[0], *sample_rate_hz_, 1);
+
+  // Remove DC level.
+  for (size_t k = 0; k < audio->num_channels(); ++k) {
+    UpdateAndRemoveDcLevel(
+        dc_forgetting_factor_, &dc_level_[k],
+        rtc::ArrayView<float>(audio->channels_f()[k], audio->num_frames()));
+  }
+
+  SignalClassifier::SignalType signal_type;
+  signal_classifier_.Analyze(*audio, &signal_type);
+  int tmp = static_cast<int>(signal_type);
+  data_dumper_->DumpRaw("lc_signal_type", 1, &tmp);
+
+  // Estimate the noise energy.
+  float noise_energy =
+      noise_level_estimator_.Analyze(signal_type, FrameEnergy(*audio));
+
+  // Estimate the overall signal peak level.
+  const float frame_peak_level = PeakLevel(*audio);
+  const float long_term_peak_level =
+      peak_level_estimator_.Analyze(signal_type, frame_peak_level);
+
+  float saturating_gain = saturating_gain_estimator_.GetGain();
+
+  // Compute the new gain to apply.
+  last_gain_ =
+      gain_selector_.GetNewGain(long_term_peak_level, noise_energy,
+                                saturating_gain, gain_jumpstart_, signal_type);
+
+  // Unflag the jumpstart of the gain as it should only happen once.
+  gain_jumpstart_ = false;
+
+  // Apply the gain to the signal.
+  int num_saturations = gain_applier_.Process(last_gain_, audio);
+
+  // Estimate the gain that saturates the overall signal.
+  saturating_gain_estimator_.Update(last_gain_, num_saturations);
+
+  // Update the metrics.
+  metrics_.Update(long_term_peak_level, noise_energy, last_gain_,
+                  frame_peak_level);
+
+  data_dumper_->DumpRaw("lc_selected_gain", 1, &last_gain_);
+  data_dumper_->DumpRaw("lc_noise_energy", 1, &noise_energy);
+  data_dumper_->DumpRaw("lc_peak_level", 1, &long_term_peak_level);
+  data_dumper_->DumpRaw("lc_saturating_gain", 1, &saturating_gain);
+
+  data_dumper_->DumpWav("lc_output", audio->num_frames(),
+                        audio->channels_f()[0], *sample_rate_hz_, 1);
+}
+
+void LevelController::ApplyConfig(
+    const AudioProcessing::Config::LevelController& config) {
+  RTC_DCHECK(Validate(config));
+  config_ = config;
+  peak_level_estimator_.Initialize(config_.initial_peak_level_dbfs);
+  gain_jumpstart_ = true;
+}
+
+std::string LevelController::ToString(
+    const AudioProcessing::Config::LevelController& config) {
+  std::stringstream ss;
+  ss << "{"
+     << "enabled: " << (config.enabled ? "true" : "false") << ", "
+     << "initial_peak_level_dbfs: " << config.initial_peak_level_dbfs << "}";
+  return ss.str();
+}
+
+bool LevelController::Validate(
+    const AudioProcessing::Config::LevelController& config) {
+  return (config.initial_peak_level_dbfs <
+              std::numeric_limits<float>::epsilon() &&
+          config.initial_peak_level_dbfs >
+              -(100.f + std::numeric_limits<float>::epsilon()));
+}
+
+}  // namespace webrtc
diff --git a/modules/audio_processing/level_controller/level_controller.h b/modules/audio_processing/level_controller/level_controller.h
new file mode 100644
index 0000000..224b886
--- /dev/null
+++ b/modules/audio_processing/level_controller/level_controller.h
@@ -0,0 +1,95 @@
+/*
+ *  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.
+ */
+
+#ifndef MODULES_AUDIO_PROCESSING_LEVEL_CONTROLLER_LEVEL_CONTROLLER_H_
+#define MODULES_AUDIO_PROCESSING_LEVEL_CONTROLLER_LEVEL_CONTROLLER_H_
+
+#include <memory>
+#include <vector>
+
+#include "api/optional.h"
+#include "modules/audio_processing/include/audio_processing.h"
+#include "modules/audio_processing/level_controller/gain_applier.h"
+#include "modules/audio_processing/level_controller/gain_selector.h"
+#include "modules/audio_processing/level_controller/noise_level_estimator.h"
+#include "modules/audio_processing/level_controller/peak_level_estimator.h"
+#include "modules/audio_processing/level_controller/saturating_gain_estimator.h"
+#include "modules/audio_processing/level_controller/signal_classifier.h"
+#include "rtc_base/constructormagic.h"
+
+namespace webrtc {
+
+class ApmDataDumper;
+class AudioBuffer;
+
+class LevelController {
+ public:
+  LevelController();
+  ~LevelController();
+
+  void Initialize(int sample_rate_hz);
+  void Process(AudioBuffer* audio);
+  float GetLastGain() { return last_gain_; }
+
+  // TODO(peah): This method is a temporary solution as the the aim is to
+  // instead apply the config inside the constructor. Therefore this is likely
+  // to change.
+  void ApplyConfig(const AudioProcessing::Config::LevelController& config);
+  // Validates a config.
+  static bool Validate(const AudioProcessing::Config::LevelController& config);
+  // Dumps a config to a string.
+  static std::string ToString(
+      const AudioProcessing::Config::LevelController& config);
+
+ private:
+  class Metrics {
+   public:
+    Metrics() { Initialize(AudioProcessing::kSampleRate48kHz); }
+    void Initialize(int sample_rate_hz);
+    void Update(float long_term_peak_level,
+                float noise_level,
+                float gain,
+                float frame_peak_level);
+
+   private:
+    void Reset();
+
+    size_t metrics_frame_counter_;
+    float gain_sum_;
+    float peak_level_sum_;
+    float noise_energy_sum_;
+    float max_gain_;
+    float max_peak_level_;
+    float max_noise_energy_;
+    float frame_length_;
+  };
+
+  std::unique_ptr<ApmDataDumper> data_dumper_;
+  GainSelector gain_selector_;
+  GainApplier gain_applier_;
+  SignalClassifier signal_classifier_;
+  NoiseLevelEstimator noise_level_estimator_;
+  PeakLevelEstimator peak_level_estimator_;
+  SaturatingGainEstimator saturating_gain_estimator_;
+  Metrics metrics_;
+  rtc::Optional<int> sample_rate_hz_;
+  static int instance_count_;
+  float dc_level_[2];
+  float dc_forgetting_factor_;
+  float last_gain_;
+  bool gain_jumpstart_ = false;
+  AudioProcessing::Config::LevelController config_;
+
+  RTC_DISALLOW_COPY_AND_ASSIGN(LevelController);
+};
+
+}  // namespace webrtc
+
+#endif  // MODULES_AUDIO_PROCESSING_LEVEL_CONTROLLER_LEVEL_CONTROLLER_H_
diff --git a/modules/audio_processing/level_controller/level_controller_complexity_unittest.cc b/modules/audio_processing/level_controller/level_controller_complexity_unittest.cc
new file mode 100644
index 0000000..83f6725
--- /dev/null
+++ b/modules/audio_processing/level_controller/level_controller_complexity_unittest.cc
@@ -0,0 +1,240 @@
+/*
+ *  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 <numeric>
+#include <vector>
+
+#include "api/array_view.h"
+#include "modules/audio_processing/audio_buffer.h"
+#include "modules/audio_processing/include/audio_processing.h"
+#include "modules/audio_processing/level_controller/level_controller.h"
+#include "modules/audio_processing/test/audio_buffer_tools.h"
+#include "modules/audio_processing/test/bitexactness_tools.h"
+#include "modules/audio_processing/test/performance_timer.h"
+#include "modules/audio_processing/test/simulator_buffers.h"
+#include "rtc_base/random.h"
+#include "system_wrappers/include/clock.h"
+#include "test/gtest.h"
+#include "test/testsupport/perf_test.h"
+
+namespace webrtc {
+namespace {
+
+const size_t kNumFramesToProcess = 300;
+const size_t kNumFramesToProcessAtWarmup = 300;
+const size_t kToTalNumFrames =
+    kNumFramesToProcess + kNumFramesToProcessAtWarmup;
+
+void RunStandaloneSubmodule(int sample_rate_hz, size_t num_channels) {
+  test::SimulatorBuffers buffers(sample_rate_hz, sample_rate_hz, sample_rate_hz,
+                                 sample_rate_hz, num_channels, num_channels,
+                                 num_channels, num_channels);
+  test::PerformanceTimer timer(kNumFramesToProcess);
+
+  LevelController level_controller;
+  level_controller.Initialize(sample_rate_hz);
+
+  for (size_t frame_no = 0; frame_no < kToTalNumFrames; ++frame_no) {
+    buffers.UpdateInputBuffers();
+
+    if (frame_no >= kNumFramesToProcessAtWarmup) {
+      timer.StartTimer();
+    }
+    level_controller.Process(buffers.capture_input_buffer.get());
+    if (frame_no >= kNumFramesToProcessAtWarmup) {
+      timer.StopTimer();
+    }
+  }
+  webrtc::test::PrintResultMeanAndError(
+      "level_controller_call_durations",
+      "_" + std::to_string(sample_rate_hz) + "Hz_" +
+          std::to_string(num_channels) + "_channels",
+      "StandaloneLevelControl", timer.GetDurationAverage(),
+      timer.GetDurationStandardDeviation(), "us", false);
+}
+
+void RunTogetherWithApm(const std::string& test_description,
+                        int render_input_sample_rate_hz,
+                        int render_output_sample_rate_hz,
+                        int capture_input_sample_rate_hz,
+                        int capture_output_sample_rate_hz,
+                        size_t num_channels,
+                        bool use_mobile_aec,
+                        bool include_default_apm_processing) {
+  test::SimulatorBuffers buffers(
+      render_input_sample_rate_hz, capture_input_sample_rate_hz,
+      render_output_sample_rate_hz, capture_output_sample_rate_hz, num_channels,
+      num_channels, num_channels, num_channels);
+  test::PerformanceTimer render_timer(kNumFramesToProcess);
+  test::PerformanceTimer capture_timer(kNumFramesToProcess);
+  test::PerformanceTimer total_timer(kNumFramesToProcess);
+
+  webrtc::Config config;
+  AudioProcessing::Config apm_config;
+  if (include_default_apm_processing) {
+    config.Set<DelayAgnostic>(new DelayAgnostic(true));
+    config.Set<ExtendedFilter>(new ExtendedFilter(true));
+  }
+  apm_config.level_controller.enabled = true;
+  apm_config.residual_echo_detector.enabled = include_default_apm_processing;
+
+  std::unique_ptr<AudioProcessing> apm;
+  apm.reset(AudioProcessingBuilder().Create(config));
+  ASSERT_TRUE(apm.get());
+  apm->ApplyConfig(apm_config);
+
+  ASSERT_EQ(AudioProcessing::kNoError,
+            apm->gain_control()->Enable(include_default_apm_processing));
+  if (use_mobile_aec) {
+    ASSERT_EQ(AudioProcessing::kNoError,
+              apm->echo_cancellation()->Enable(false));
+    ASSERT_EQ(AudioProcessing::kNoError, apm->echo_control_mobile()->Enable(
+                                             include_default_apm_processing));
+  } else {
+    ASSERT_EQ(AudioProcessing::kNoError,
+              apm->echo_cancellation()->Enable(include_default_apm_processing));
+    ASSERT_EQ(AudioProcessing::kNoError,
+              apm->echo_control_mobile()->Enable(false));
+  }
+  apm_config.high_pass_filter.enabled = include_default_apm_processing;
+  ASSERT_EQ(AudioProcessing::kNoError,
+            apm->noise_suppression()->Enable(include_default_apm_processing));
+  ASSERT_EQ(AudioProcessing::kNoError,
+            apm->voice_detection()->Enable(include_default_apm_processing));
+  ASSERT_EQ(AudioProcessing::kNoError,
+            apm->level_estimator()->Enable(include_default_apm_processing));
+
+  StreamConfig render_input_config(render_input_sample_rate_hz, num_channels,
+                                   false);
+  StreamConfig render_output_config(render_output_sample_rate_hz, num_channels,
+                                    false);
+  StreamConfig capture_input_config(capture_input_sample_rate_hz, num_channels,
+                                    false);
+  StreamConfig capture_output_config(capture_output_sample_rate_hz,
+                                     num_channels, false);
+
+  for (size_t frame_no = 0; frame_no < kToTalNumFrames; ++frame_no) {
+    buffers.UpdateInputBuffers();
+
+    if (frame_no >= kNumFramesToProcessAtWarmup) {
+      total_timer.StartTimer();
+      render_timer.StartTimer();
+    }
+    ASSERT_EQ(AudioProcessing::kNoError,
+              apm->ProcessReverseStream(
+                  &buffers.render_input[0], render_input_config,
+                  render_output_config, &buffers.render_output[0]));
+
+    if (frame_no >= kNumFramesToProcessAtWarmup) {
+      render_timer.StopTimer();
+
+      capture_timer.StartTimer();
+    }
+
+    ASSERT_EQ(AudioProcessing::kNoError, apm->set_stream_delay_ms(0));
+    ASSERT_EQ(
+        AudioProcessing::kNoError,
+        apm->ProcessStream(&buffers.capture_input[0], capture_input_config,
+                           capture_output_config, &buffers.capture_output[0]));
+
+    if (frame_no >= kNumFramesToProcessAtWarmup) {
+      capture_timer.StopTimer();
+      total_timer.StopTimer();
+    }
+  }
+
+  webrtc::test::PrintResultMeanAndError(
+      "level_controller_call_durations",
+      "_" + std::to_string(render_input_sample_rate_hz) + "_" +
+          std::to_string(render_output_sample_rate_hz) + "_" +
+          std::to_string(capture_input_sample_rate_hz) + "_" +
+          std::to_string(capture_output_sample_rate_hz) + "Hz_" +
+          std::to_string(num_channels) + "_channels" + "_render",
+      test_description, render_timer.GetDurationAverage(),
+      render_timer.GetDurationStandardDeviation(), "us", false);
+  webrtc::test::PrintResultMeanAndError(
+      "level_controller_call_durations",
+      "_" + std::to_string(render_input_sample_rate_hz) + "_" +
+          std::to_string(render_output_sample_rate_hz) + "_" +
+          std::to_string(capture_input_sample_rate_hz) + "_" +
+          std::to_string(capture_output_sample_rate_hz) + "Hz_" +
+          std::to_string(num_channels) + "_channels" + "_capture",
+      test_description, capture_timer.GetDurationAverage(),
+      capture_timer.GetDurationStandardDeviation(), "us", false);
+  webrtc::test::PrintResultMeanAndError(
+      "level_controller_call_durations",
+      "_" + std::to_string(render_input_sample_rate_hz) + "_" +
+          std::to_string(render_output_sample_rate_hz) + "_" +
+          std::to_string(capture_input_sample_rate_hz) + "_" +
+          std::to_string(capture_output_sample_rate_hz) + "Hz_" +
+          std::to_string(num_channels) + "_channels" + "_total",
+      test_description, total_timer.GetDurationAverage(),
+      total_timer.GetDurationStandardDeviation(), "us", false);
+}
+
+}  // namespace
+
+// TODO(peah): Reactivate once issue 7712 has been resolved.
+TEST(LevelControllerPerformanceTest, DISABLED_StandaloneProcessing) {
+  int sample_rates_to_test[] = {
+      AudioProcessing::kSampleRate8kHz, AudioProcessing::kSampleRate16kHz,
+      AudioProcessing::kSampleRate32kHz, AudioProcessing::kSampleRate48kHz};
+  for (auto sample_rate : sample_rates_to_test) {
+    for (size_t num_channels = 1; num_channels <= 2; ++num_channels) {
+      RunStandaloneSubmodule(sample_rate, num_channels);
+    }
+  }
+}
+
+void TestSomeSampleRatesWithApm(const std::string& test_name,
+                                bool use_mobile_agc,
+                                bool include_default_apm_processing) {
+  // Test some stereo combinations first.
+  size_t num_channels = 2;
+  RunTogetherWithApm(test_name, 48000, 48000, AudioProcessing::kSampleRate16kHz,
+                     AudioProcessing::kSampleRate32kHz, num_channels,
+                     use_mobile_agc, include_default_apm_processing);
+  RunTogetherWithApm(test_name, 48000, 48000, AudioProcessing::kSampleRate48kHz,
+                     AudioProcessing::kSampleRate8kHz, num_channels,
+                     use_mobile_agc, include_default_apm_processing);
+  RunTogetherWithApm(test_name, 48000, 48000, 44100, 44100, num_channels,
+                     use_mobile_agc, include_default_apm_processing);
+
+  // Then test mono combinations.
+  num_channels = 1;
+  RunTogetherWithApm(test_name, 48000, 48000, AudioProcessing::kSampleRate48kHz,
+                     AudioProcessing::kSampleRate48kHz, num_channels,
+                     use_mobile_agc, include_default_apm_processing);
+}
+
+// TODO(peah): Reactivate once issue 7712 has been resolved.
+#if !defined(WEBRTC_ANDROID)
+TEST(LevelControllerPerformanceTest, DISABLED_ProcessingViaApm) {
+#else
+TEST(LevelControllerPerformanceTest, DISABLED_ProcessingViaApm) {
+#endif
+  // Run without default APM processing and desktop AGC.
+  TestSomeSampleRatesWithApm("SimpleLevelControlViaApm", false, false);
+}
+
+// TODO(peah): Reactivate once issue 7712 has been resolved.
+#if !defined(WEBRTC_ANDROID)
+TEST(LevelControllerPerformanceTest, DISABLED_InteractionWithDefaultApm) {
+#else
+TEST(LevelControllerPerformanceTest, DISABLED_InteractionWithDefaultApm) {
+#endif
+  bool include_default_apm_processing = true;
+  TestSomeSampleRatesWithApm("LevelControlAndDefaultDesktopApm", false,
+                             include_default_apm_processing);
+  TestSomeSampleRatesWithApm("LevelControlAndDefaultMobileApm", true,
+                             include_default_apm_processing);
+}
+
+}  // namespace webrtc
diff --git a/modules/audio_processing/level_controller/level_controller_constants.h b/modules/audio_processing/level_controller/level_controller_constants.h
new file mode 100644
index 0000000..6cf2cd4
--- /dev/null
+++ b/modules/audio_processing/level_controller/level_controller_constants.h
@@ -0,0 +1,23 @@
+/*
+ *  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.
+ */
+
+#ifndef MODULES_AUDIO_PROCESSING_LEVEL_CONTROLLER_LEVEL_CONTROLLER_CONSTANTS_H_
+#define MODULES_AUDIO_PROCESSING_LEVEL_CONTROLLER_LEVEL_CONTROLLER_CONSTANTS_H_
+
+namespace webrtc {
+
+const float kMaxLcGain = 10;
+const float kMaxLcNoisePower = 100.f * 100.f;
+const float kTargetLcPeakLevel = 16384.f;
+const float kTargetLcPeakLeveldBFS = -6.0206f;
+
+}  // namespace webrtc
+
+#endif  // MODULES_AUDIO_PROCESSING_LEVEL_CONTROLLER_LEVEL_CONTROLLER_CONSTANTS_H_
diff --git a/modules/audio_processing/level_controller/level_controller_unittest.cc b/modules/audio_processing/level_controller/level_controller_unittest.cc
new file mode 100644
index 0000000..cb36ae0
--- /dev/null
+++ b/modules/audio_processing/level_controller/level_controller_unittest.cc
@@ -0,0 +1,156 @@
+/*
+ *  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 <vector>
+
+#include "api/array_view.h"
+#include "api/optional.h"
+#include "modules/audio_processing/audio_buffer.h"
+#include "modules/audio_processing/include/audio_processing.h"
+#include "modules/audio_processing/level_controller/level_controller.h"
+#include "modules/audio_processing/test/audio_buffer_tools.h"
+#include "modules/audio_processing/test/bitexactness_tools.h"
+#include "test/gtest.h"
+
+namespace webrtc {
+namespace {
+
+const int kNumFramesToProcess = 1000;
+
+// Processes a specified amount of frames, verifies the results and reports
+// any errors.
+void RunBitexactnessTest(int sample_rate_hz,
+                         size_t num_channels,
+                         rtc::Optional<float> initial_peak_level_dbfs,
+                         rtc::ArrayView<const float> output_reference) {
+  LevelController level_controller;
+  level_controller.Initialize(sample_rate_hz);
+  if (initial_peak_level_dbfs) {
+    AudioProcessing::Config::LevelController config;
+    config.initial_peak_level_dbfs = *initial_peak_level_dbfs;
+    level_controller.ApplyConfig(config);
+  }
+
+  int samples_per_channel = rtc::CheckedDivExact(sample_rate_hz, 100);
+  const StreamConfig capture_config(sample_rate_hz, num_channels, false);
+  AudioBuffer capture_buffer(
+      capture_config.num_frames(), capture_config.num_channels(),
+      capture_config.num_frames(), capture_config.num_channels(),
+      capture_config.num_frames());
+  test::InputAudioFile capture_file(
+      test::GetApmCaptureTestVectorFileName(sample_rate_hz));
+  std::vector<float> capture_input(samples_per_channel * num_channels);
+  for (size_t frame_no = 0; frame_no < kNumFramesToProcess; ++frame_no) {
+    ReadFloatSamplesFromStereoFile(samples_per_channel, num_channels,
+                                   &capture_file, capture_input);
+
+    test::CopyVectorToAudioBuffer(capture_config, capture_input,
+                                  &capture_buffer);
+
+    level_controller.Process(&capture_buffer);
+  }
+
+  // Extract test results.
+  std::vector<float> capture_output;
+  test::ExtractVectorFromAudioBuffer(capture_config, &capture_buffer,
+                                     &capture_output);
+
+  // Compare the output with the reference. Only the first values of the output
+  // from last frame processed are compared in order not having to specify all
+  // preceding frames as testvectors. As the algorithm being tested has a
+  // memory, testing only the last frame implicitly also tests the preceeding
+  // frames.
+  const float kVectorElementErrorBound = 1.0f / 32768.0f;
+  EXPECT_TRUE(test::VerifyDeinterleavedArray(
+      capture_config.num_frames(), capture_config.num_channels(),
+      output_reference, capture_output, kVectorElementErrorBound));
+}
+
+}  // namespace
+
+TEST(LevelControllerConfig, ToString) {
+  AudioProcessing::Config config;
+  config.level_controller.enabled = true;
+  config.level_controller.initial_peak_level_dbfs = -6.0206f;
+  EXPECT_EQ("{enabled: true, initial_peak_level_dbfs: -6.0206}",
+            LevelController::ToString(config.level_controller));
+
+  config.level_controller.enabled = false;
+  config.level_controller.initial_peak_level_dbfs = -50.f;
+  EXPECT_EQ("{enabled: false, initial_peak_level_dbfs: -50}",
+            LevelController::ToString(config.level_controller));
+}
+
+TEST(LevelControlBitExactnessTest, Mono8kHz) {
+  const float kOutputReference[] = {-0.013939f, -0.012154f, -0.009054f};
+  RunBitexactnessTest(AudioProcessing::kSampleRate8kHz, 1, rtc::nullopt,
+                      kOutputReference);
+}
+
+TEST(LevelControlBitExactnessTest, Mono16kHz) {
+  const float kOutputReference[] = {-0.013706f, -0.013215f, -0.013018f};
+  RunBitexactnessTest(AudioProcessing::kSampleRate16kHz, 1, rtc::nullopt,
+                      kOutputReference);
+}
+
+TEST(LevelControlBitExactnessTest, Mono32kHz) {
+  const float kOutputReference[] = {-0.014495f, -0.016425f, -0.016085f};
+  RunBitexactnessTest(AudioProcessing::kSampleRate32kHz, 1, rtc::nullopt,
+                      kOutputReference);
+}
+
+// TODO(peah): Investigate why this particular testcase differ between Android
+// and the rest of the platforms.
+TEST(LevelControlBitExactnessTest, Mono48kHz) {
+#if !(defined(WEBRTC_ARCH_ARM64) || defined(WEBRTC_ARCH_ARM) || \
+      defined(WEBRTC_ANDROID))
+  const float kOutputReference[] = {-0.014277f, -0.015180f, -0.017437f};
+#else
+  const float kOutputReference[] = {-0.014306f, -0.015209f, -0.017466f};
+#endif
+  RunBitexactnessTest(AudioProcessing::kSampleRate48kHz, 1, rtc::nullopt,
+                      kOutputReference);
+}
+
+TEST(LevelControlBitExactnessTest, Stereo8kHz) {
+  const float kOutputReference[] = {-0.014063f, -0.008450f, -0.012159f,
+                                    -0.051967f, -0.023202f, -0.047858f};
+  RunBitexactnessTest(AudioProcessing::kSampleRate8kHz, 2, rtc::nullopt,
+                      kOutputReference);
+}
+
+TEST(LevelControlBitExactnessTest, Stereo16kHz) {
+  const float kOutputReference[] = {-0.012714f, -0.005896f, -0.012220f,
+                                    -0.053306f, -0.024549f, -0.051527f};
+  RunBitexactnessTest(AudioProcessing::kSampleRate16kHz, 2, rtc::nullopt,
+                      kOutputReference);
+}
+
+TEST(LevelControlBitExactnessTest, Stereo32kHz) {
+  const float kOutputReference[] = {-0.011764f, -0.007044f, -0.013472f,
+                                    -0.053537f, -0.026322f, -0.056253f};
+  RunBitexactnessTest(AudioProcessing::kSampleRate32kHz, 2, rtc::nullopt,
+                      kOutputReference);
+}
+
+TEST(LevelControlBitExactnessTest, Stereo48kHz) {
+  const float kOutputReference[] = {-0.010643f, -0.006334f, -0.011377f,
+                                    -0.049088f, -0.023600f, -0.050465f};
+  RunBitexactnessTest(AudioProcessing::kSampleRate48kHz, 2, rtc::nullopt,
+                      kOutputReference);
+}
+
+TEST(LevelControlBitExactnessTest, MonoInitial48kHz) {
+  const float kOutputReference[] = {-0.013884f, -0.014761f, -0.016951f};
+  RunBitexactnessTest(AudioProcessing::kSampleRate48kHz, 1, -50,
+                      kOutputReference);
+}
+
+}  // namespace webrtc
diff --git a/modules/audio_processing/level_controller/noise_level_estimator.cc b/modules/audio_processing/level_controller/noise_level_estimator.cc
new file mode 100644
index 0000000..abf4ea2
--- /dev/null
+++ b/modules/audio_processing/level_controller/noise_level_estimator.cc
@@ -0,0 +1,72 @@
+/*
+ *  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 "modules/audio_processing/level_controller/noise_level_estimator.h"
+
+#include <algorithm>
+
+#include "modules/audio_processing/audio_buffer.h"
+#include "modules/audio_processing/logging/apm_data_dumper.h"
+
+namespace webrtc {
+
+NoiseLevelEstimator::NoiseLevelEstimator() {
+  Initialize(AudioProcessing::kSampleRate48kHz);
+}
+
+NoiseLevelEstimator::~NoiseLevelEstimator() {}
+
+void NoiseLevelEstimator::Initialize(int sample_rate_hz) {
+  noise_energy_ = 1.f;
+  first_update_ = true;
+  min_noise_energy_ = sample_rate_hz * 2.f * 2.f / 100.f;
+  noise_energy_hold_counter_ = 0;
+}
+
+float NoiseLevelEstimator::Analyze(SignalClassifier::SignalType signal_type,
+                                   float frame_energy) {
+  if (frame_energy <= 0.f) {
+    return noise_energy_;
+  }
+
+  if (first_update_) {
+    // Initialize the noise energy to the frame energy.
+    first_update_ = false;
+    return noise_energy_ = std::max(frame_energy, min_noise_energy_);
+  }
+
+  // Update the noise estimate in a minimum statistics-type manner.
+  if (signal_type == SignalClassifier::SignalType::kStationary) {
+    if (frame_energy > noise_energy_) {
+      // Leak the estimate upwards towards the frame energy if no recent
+      // downward update.
+      noise_energy_hold_counter_ = std::max(noise_energy_hold_counter_ - 1, 0);
+
+      if (noise_energy_hold_counter_ == 0) {
+        noise_energy_ = std::min(noise_energy_ * 1.01f, frame_energy);
+      }
+    } else {
+      // Update smoothly downwards with a limited maximum update magnitude.
+      noise_energy_ =
+          std::max(noise_energy_ * 0.9f,
+                   noise_energy_ + 0.05f * (frame_energy - noise_energy_));
+      noise_energy_hold_counter_ = 1000;
+    }
+  } else {
+    // For a non-stationary signal, leak the estimate downwards in order to
+    // avoid estimate locking due to incorrect signal classification.
+    noise_energy_ = noise_energy_ * 0.99f;
+  }
+
+  // Ensure a minimum of the estimate.
+  return noise_energy_ = std::max(noise_energy_, min_noise_energy_);
+}
+
+}  // namespace webrtc
diff --git a/modules/audio_processing/level_controller/noise_level_estimator.h b/modules/audio_processing/level_controller/noise_level_estimator.h
new file mode 100644
index 0000000..94ef673
--- /dev/null
+++ b/modules/audio_processing/level_controller/noise_level_estimator.h
@@ -0,0 +1,37 @@
+/*
+ *  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.
+ */
+
+#ifndef MODULES_AUDIO_PROCESSING_LEVEL_CONTROLLER_NOISE_LEVEL_ESTIMATOR_H_
+#define MODULES_AUDIO_PROCESSING_LEVEL_CONTROLLER_NOISE_LEVEL_ESTIMATOR_H_
+
+#include "modules/audio_processing/level_controller/signal_classifier.h"
+#include "rtc_base/constructormagic.h"
+
+namespace webrtc {
+
+class NoiseLevelEstimator {
+ public:
+  NoiseLevelEstimator();
+  ~NoiseLevelEstimator();
+  void Initialize(int sample_rate_hz);
+  float Analyze(SignalClassifier::SignalType signal_type, float frame_energy);
+
+ private:
+  float min_noise_energy_ = 0.f;
+  bool first_update_;
+  float noise_energy_;
+  int noise_energy_hold_counter_;
+
+  RTC_DISALLOW_COPY_AND_ASSIGN(NoiseLevelEstimator);
+};
+
+}  // namespace webrtc
+
+#endif  // MODULES_AUDIO_PROCESSING_LEVEL_CONTROLLER_NOISE_LEVEL_ESTIMATOR_H_
diff --git a/modules/audio_processing/level_controller/noise_spectrum_estimator.cc b/modules/audio_processing/level_controller/noise_spectrum_estimator.cc
new file mode 100644
index 0000000..6e921c2
--- /dev/null
+++ b/modules/audio_processing/level_controller/noise_spectrum_estimator.cc
@@ -0,0 +1,68 @@
+/*
+ *  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 "modules/audio_processing/level_controller/noise_spectrum_estimator.h"
+
+#include <string.h>
+#include <algorithm>
+
+#include "api/array_view.h"
+#include "modules/audio_processing/logging/apm_data_dumper.h"
+#include "rtc_base/arraysize.h"
+
+namespace webrtc {
+namespace {
+constexpr float kMinNoisePower = 100.f;
+}  // namespace
+
+NoiseSpectrumEstimator::NoiseSpectrumEstimator(ApmDataDumper* data_dumper)
+    : data_dumper_(data_dumper) {
+  Initialize();
+}
+
+void NoiseSpectrumEstimator::Initialize() {
+  std::fill(noise_spectrum_, noise_spectrum_ + arraysize(noise_spectrum_),
+            kMinNoisePower);
+}
+
+void NoiseSpectrumEstimator::Update(rtc::ArrayView<const float> spectrum,
+                                    bool first_update) {
+  RTC_DCHECK_EQ(65, spectrum.size());
+
+  if (first_update) {
+    // Initialize the noise spectral estimate with the signal spectrum.
+    std::copy(spectrum.data(), spectrum.data() + spectrum.size(),
+              noise_spectrum_);
+  } else {
+    // Smoothly update the noise spectral estimate towards the signal spectrum
+    // such that the magnitude of the updates are limited.
+    for (size_t k = 0; k < spectrum.size(); ++k) {
+      if (noise_spectrum_[k] < spectrum[k]) {
+        noise_spectrum_[k] = std::min(
+            1.01f * noise_spectrum_[k],
+            noise_spectrum_[k] + 0.05f * (spectrum[k] - noise_spectrum_[k]));
+      } else {
+        noise_spectrum_[k] = std::max(
+            0.99f * noise_spectrum_[k],
+            noise_spectrum_[k] + 0.05f * (spectrum[k] - noise_spectrum_[k]));
+      }
+    }
+  }
+
+  // Ensure that the noise spectal estimate does not become too low.
+  for (auto& v : noise_spectrum_) {
+    v = std::max(v, kMinNoisePower);
+  }
+
+  data_dumper_->DumpRaw("lc_noise_spectrum", 65, noise_spectrum_);
+  data_dumper_->DumpRaw("lc_signal_spectrum", spectrum);
+}
+
+}  // namespace webrtc
diff --git a/modules/audio_processing/level_controller/noise_spectrum_estimator.h b/modules/audio_processing/level_controller/noise_spectrum_estimator.h
new file mode 100644
index 0000000..f10933e
--- /dev/null
+++ b/modules/audio_processing/level_controller/noise_spectrum_estimator.h
@@ -0,0 +1,40 @@
+/*
+ *  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.
+ */
+
+#ifndef MODULES_AUDIO_PROCESSING_LEVEL_CONTROLLER_NOISE_SPECTRUM_ESTIMATOR_H_
+#define MODULES_AUDIO_PROCESSING_LEVEL_CONTROLLER_NOISE_SPECTRUM_ESTIMATOR_H_
+
+#include "api/array_view.h"
+#include "rtc_base/constructormagic.h"
+
+namespace webrtc {
+
+class ApmDataDumper;
+
+class NoiseSpectrumEstimator {
+ public:
+  explicit NoiseSpectrumEstimator(ApmDataDumper* data_dumper);
+  void Initialize();
+  void Update(rtc::ArrayView<const float> spectrum, bool first_update);
+
+  rtc::ArrayView<const float> GetNoiseSpectrum() const {
+    return rtc::ArrayView<const float>(noise_spectrum_);
+  }
+
+ private:
+  ApmDataDumper* data_dumper_;
+  float noise_spectrum_[65];
+
+  RTC_DISALLOW_IMPLICIT_CONSTRUCTORS(NoiseSpectrumEstimator);
+};
+
+}  // namespace webrtc
+
+#endif  // MODULES_AUDIO_PROCESSING_LEVEL_CONTROLLER_NOISE_SPECTRUM_ESTIMATOR_H_
diff --git a/modules/audio_processing/level_controller/peak_level_estimator.cc b/modules/audio_processing/level_controller/peak_level_estimator.cc
new file mode 100644
index 0000000..f602892
--- /dev/null
+++ b/modules/audio_processing/level_controller/peak_level_estimator.cc
@@ -0,0 +1,74 @@
+/*
+ *  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 "modules/audio_processing/level_controller/peak_level_estimator.h"
+
+#include <algorithm>
+
+#include "common_audio/include/audio_util.h"
+#include "modules/audio_processing/audio_buffer.h"
+#include "modules/audio_processing/logging/apm_data_dumper.h"
+
+namespace webrtc {
+namespace {
+
+constexpr float kMinLevel = 30.f;
+
+}  // namespace
+
+PeakLevelEstimator::PeakLevelEstimator(float initial_peak_level_dbfs) {
+  Initialize(initial_peak_level_dbfs);
+}
+
+PeakLevelEstimator::~PeakLevelEstimator() {}
+
+void PeakLevelEstimator::Initialize(float initial_peak_level_dbfs) {
+  RTC_DCHECK_LE(-100.f, initial_peak_level_dbfs);
+  RTC_DCHECK_GE(0.f, initial_peak_level_dbfs);
+
+  peak_level_ = std::max(DbfsToFloatS16(initial_peak_level_dbfs), kMinLevel);
+
+  hold_counter_ = 0;
+  initialization_phase_ = true;
+}
+
+float PeakLevelEstimator::Analyze(SignalClassifier::SignalType signal_type,
+                                  float frame_peak_level) {
+  if (frame_peak_level == 0) {
+    RTC_DCHECK_LE(kMinLevel, peak_level_);
+    return peak_level_;
+  }
+
+  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;
+    initialization_phase_ = false;
+  } 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) ||
+        initialization_phase_) {
+      peak_level_ =
+          std::max(peak_level_ + 0.01f * (frame_peak_level - peak_level_),
+                   peak_level_ * 0.995f);
+    }
+  }
+
+  peak_level_ = std::max(peak_level_, kMinLevel);
+
+  return peak_level_;
+}
+
+}  // namespace webrtc
diff --git a/modules/audio_processing/level_controller/peak_level_estimator.h b/modules/audio_processing/level_controller/peak_level_estimator.h
new file mode 100644
index 0000000..0aa55d2
--- /dev/null
+++ b/modules/audio_processing/level_controller/peak_level_estimator.h
@@ -0,0 +1,37 @@
+/*
+ *  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.
+ */
+
+#ifndef MODULES_AUDIO_PROCESSING_LEVEL_CONTROLLER_PEAK_LEVEL_ESTIMATOR_H_
+#define MODULES_AUDIO_PROCESSING_LEVEL_CONTROLLER_PEAK_LEVEL_ESTIMATOR_H_
+
+#include "modules/audio_processing/level_controller/level_controller_constants.h"
+#include "modules/audio_processing/level_controller/signal_classifier.h"
+#include "rtc_base/constructormagic.h"
+
+namespace webrtc {
+
+class PeakLevelEstimator {
+ public:
+  explicit PeakLevelEstimator(float initial_peak_level_dbfs);
+  ~PeakLevelEstimator();
+  void Initialize(float initial_peak_level_dbfs);
+  float Analyze(SignalClassifier::SignalType signal_type,
+                float frame_peak_level);
+ private:
+  float peak_level_;
+  int hold_counter_;
+  bool initialization_phase_;
+
+  RTC_DISALLOW_IMPLICIT_CONSTRUCTORS(PeakLevelEstimator);
+};
+
+}  // namespace webrtc
+
+#endif  // MODULES_AUDIO_PROCESSING_LEVEL_CONTROLLER_PEAK_LEVEL_ESTIMATOR_H_
diff --git a/modules/audio_processing/level_controller/saturating_gain_estimator.cc b/modules/audio_processing/level_controller/saturating_gain_estimator.cc
new file mode 100644
index 0000000..60110c6
--- /dev/null
+++ b/modules/audio_processing/level_controller/saturating_gain_estimator.cc
@@ -0,0 +1,48 @@
+/*
+ *  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 "modules/audio_processing/level_controller/saturating_gain_estimator.h"
+
+#include <math.h>
+#include <algorithm>
+
+#include "modules/audio_processing/level_controller/level_controller_constants.h"
+#include "modules/audio_processing/logging/apm_data_dumper.h"
+
+namespace webrtc {
+
+SaturatingGainEstimator::SaturatingGainEstimator() {
+  Initialize();
+}
+
+SaturatingGainEstimator::~SaturatingGainEstimator() {}
+
+void SaturatingGainEstimator::Initialize() {
+  saturating_gain_ = kMaxLcGain;
+  saturating_gain_hold_counter_ = 0;
+}
+
+void SaturatingGainEstimator::Update(float gain, int num_saturations) {
+  bool too_many_saturations = (num_saturations > 2);
+
+  if (too_many_saturations) {
+    saturating_gain_ = 0.95f * gain;
+    saturating_gain_hold_counter_ = 1000;
+  } else {
+    saturating_gain_hold_counter_ =
+        std::max(0, saturating_gain_hold_counter_ - 1);
+    if (saturating_gain_hold_counter_ == 0) {
+      saturating_gain_ *= 1.001f;
+      saturating_gain_ = std::min(kMaxLcGain, saturating_gain_);
+    }
+  }
+}
+
+}  // namespace webrtc
diff --git a/modules/audio_processing/level_controller/saturating_gain_estimator.h b/modules/audio_processing/level_controller/saturating_gain_estimator.h
new file mode 100644
index 0000000..8980f4e
--- /dev/null
+++ b/modules/audio_processing/level_controller/saturating_gain_estimator.h
@@ -0,0 +1,37 @@
+/*
+ *  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.
+ */
+
+#ifndef MODULES_AUDIO_PROCESSING_LEVEL_CONTROLLER_SATURATING_GAIN_ESTIMATOR_H_
+#define MODULES_AUDIO_PROCESSING_LEVEL_CONTROLLER_SATURATING_GAIN_ESTIMATOR_H_
+
+#include "rtc_base/constructormagic.h"
+
+namespace webrtc {
+
+class ApmDataDumper;
+
+class SaturatingGainEstimator {
+ public:
+  SaturatingGainEstimator();
+  ~SaturatingGainEstimator();
+  void Initialize();
+  void Update(float gain, int num_saturations);
+  float GetGain() const { return saturating_gain_; }
+
+ private:
+  float saturating_gain_;
+  int saturating_gain_hold_counter_;
+
+  RTC_DISALLOW_COPY_AND_ASSIGN(SaturatingGainEstimator);
+};
+
+}  // namespace webrtc
+
+#endif  // MODULES_AUDIO_PROCESSING_LEVEL_CONTROLLER_SATURATING_GAIN_ESTIMATOR_H_
diff --git a/modules/audio_processing/level_controller/signal_classifier.cc b/modules/audio_processing/level_controller/signal_classifier.cc
new file mode 100644
index 0000000..d2d5917
--- /dev/null
+++ b/modules/audio_processing/level_controller/signal_classifier.cc
@@ -0,0 +1,171 @@
+/*
+ *  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 "modules/audio_processing/level_controller/signal_classifier.h"
+
+#include <algorithm>
+#include <numeric>
+#include <vector>
+
+#include "api/array_view.h"
+#include "modules/audio_processing/audio_buffer.h"
+#include "modules/audio_processing/level_controller/down_sampler.h"
+#include "modules/audio_processing/level_controller/noise_spectrum_estimator.h"
+#include "modules/audio_processing/logging/apm_data_dumper.h"
+#include "rtc_base/constructormagic.h"
+
+namespace webrtc {
+namespace {
+
+void RemoveDcLevel(rtc::ArrayView<float> x) {
+  RTC_DCHECK_LT(0, x.size());
+  float mean = std::accumulate(x.data(), x.data() + x.size(), 0.f);
+  mean /= x.size();
+
+  for (float& v : x) {
+    v -= mean;
+  }
+}
+
+void PowerSpectrum(const OouraFft* ooura_fft,
+                   rtc::ArrayView<const float> x,
+                   rtc::ArrayView<float> spectrum) {
+  RTC_DCHECK_EQ(65, spectrum.size());
+  RTC_DCHECK_EQ(128, x.size());
+  float X[128];
+  std::copy(x.data(), x.data() + x.size(), X);
+  ooura_fft->Fft(X);
+
+  float* X_p = X;
+  RTC_DCHECK_EQ(X_p, &X[0]);
+  spectrum[0] = (*X_p) * (*X_p);
+  ++X_p;
+  RTC_DCHECK_EQ(X_p, &X[1]);
+  spectrum[64] = (*X_p) * (*X_p);
+  for (int k = 1; k < 64; ++k) {
+    ++X_p;
+    RTC_DCHECK_EQ(X_p, &X[2 * k]);
+    spectrum[k] = (*X_p) * (*X_p);
+    ++X_p;
+    RTC_DCHECK_EQ(X_p, &X[2 * k + 1]);
+    spectrum[k] += (*X_p) * (*X_p);
+  }
+}
+
+webrtc::SignalClassifier::SignalType ClassifySignal(
+    rtc::ArrayView<const float> signal_spectrum,
+    rtc::ArrayView<const float> noise_spectrum,
+    ApmDataDumper* data_dumper) {
+  int num_stationary_bands = 0;
+  int num_highly_nonstationary_bands = 0;
+
+  // Detect stationary and highly nonstationary bands.
+  for (size_t k = 1; k < 40; k++) {
+    if (signal_spectrum[k] < 3 * noise_spectrum[k] &&
+        signal_spectrum[k] * 3 > noise_spectrum[k]) {
+      ++num_stationary_bands;
+    } else if (signal_spectrum[k] > 9 * noise_spectrum[k]) {
+      ++num_highly_nonstationary_bands;
+    }
+  }
+
+  data_dumper->DumpRaw("lc_num_stationary_bands", 1, &num_stationary_bands);
+  data_dumper->DumpRaw("lc_num_highly_nonstationary_bands", 1,
+                       &num_highly_nonstationary_bands);
+
+  // Use the detected number of bands to classify the overall signal
+  // stationarity.
+  if (num_stationary_bands > 15) {
+    return SignalClassifier::SignalType::kStationary;
+  } else if (num_highly_nonstationary_bands > 15) {
+    return SignalClassifier::SignalType::kHighlyNonStationary;
+  } else {
+    return SignalClassifier::SignalType::kNonStationary;
+  }
+}
+
+}  // namespace
+
+SignalClassifier::FrameExtender::FrameExtender(size_t frame_size,
+                                               size_t extended_frame_size)
+    : x_old_(extended_frame_size - frame_size, 0.f) {}
+
+SignalClassifier::FrameExtender::~FrameExtender() = default;
+
+void SignalClassifier::FrameExtender::ExtendFrame(
+    rtc::ArrayView<const float> x,
+    rtc::ArrayView<float> x_extended) {
+  RTC_DCHECK_EQ(x_old_.size() + x.size(), x_extended.size());
+  std::copy(x_old_.data(), x_old_.data() + x_old_.size(), x_extended.data());
+  std::copy(x.data(), x.data() + x.size(), x_extended.data() + x_old_.size());
+  std::copy(x_extended.data() + x_extended.size() - x_old_.size(),
+            x_extended.data() + x_extended.size(), x_old_.data());
+}
+
+SignalClassifier::SignalClassifier(ApmDataDumper* data_dumper)
+    : data_dumper_(data_dumper),
+      down_sampler_(data_dumper_),
+      noise_spectrum_estimator_(data_dumper_) {
+  Initialize(AudioProcessing::kSampleRate48kHz);
+}
+SignalClassifier::~SignalClassifier() {}
+
+void SignalClassifier::Initialize(int sample_rate_hz) {
+  down_sampler_.Initialize(sample_rate_hz);
+  noise_spectrum_estimator_.Initialize();
+  frame_extender_.reset(new FrameExtender(80, 128));
+  sample_rate_hz_ = sample_rate_hz;
+  initialization_frames_left_ = 2;
+  consistent_classification_counter_ = 3;
+  last_signal_type_ = SignalClassifier::SignalType::kNonStationary;
+}
+
+void SignalClassifier::Analyze(const AudioBuffer& audio,
+                               SignalType* signal_type) {
+  RTC_DCHECK_EQ(audio.num_frames(), sample_rate_hz_ / 100);
+
+  // Compute the signal power spectrum.
+  float downsampled_frame[80];
+  down_sampler_.DownSample(rtc::ArrayView<const float>(
+                               audio.channels_const_f()[0], audio.num_frames()),
+                           downsampled_frame);
+  float extended_frame[128];
+  frame_extender_->ExtendFrame(downsampled_frame, extended_frame);
+  RemoveDcLevel(extended_frame);
+  float signal_spectrum[65];
+  PowerSpectrum(&ooura_fft_, extended_frame, signal_spectrum);
+
+  // Classify the signal based on the estimate of the noise spectrum and the
+  // signal spectrum estimate.
+  *signal_type = ClassifySignal(signal_spectrum,
+                                noise_spectrum_estimator_.GetNoiseSpectrum(),
+                                data_dumper_);
+
+  // Update the noise spectrum based on the signal spectrum.
+  noise_spectrum_estimator_.Update(signal_spectrum,
+                                   initialization_frames_left_ > 0);
+
+  // Update the number of frames until a reliable signal spectrum is achieved.
+  initialization_frames_left_ = std::max(0, initialization_frames_left_ - 1);
+
+  if (last_signal_type_ == *signal_type) {
+    consistent_classification_counter_ =
+        std::max(0, consistent_classification_counter_ - 1);
+  } else {
+    last_signal_type_ = *signal_type;
+    consistent_classification_counter_ = 3;
+  }
+
+  if (consistent_classification_counter_ > 0) {
+    *signal_type = SignalClassifier::SignalType::kNonStationary;
+  }
+}
+
+}  // namespace webrtc
diff --git a/modules/audio_processing/level_controller/signal_classifier.h b/modules/audio_processing/level_controller/signal_classifier.h
new file mode 100644
index 0000000..2be13fe
--- /dev/null
+++ b/modules/audio_processing/level_controller/signal_classifier.h
@@ -0,0 +1,67 @@
+/*
+ *  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.
+ */
+
+#ifndef MODULES_AUDIO_PROCESSING_LEVEL_CONTROLLER_SIGNAL_CLASSIFIER_H_
+#define MODULES_AUDIO_PROCESSING_LEVEL_CONTROLLER_SIGNAL_CLASSIFIER_H_
+
+#include <memory>
+#include <vector>
+
+#include "api/array_view.h"
+#include "modules/audio_processing/level_controller/down_sampler.h"
+#include "modules/audio_processing/level_controller/noise_spectrum_estimator.h"
+#include "modules/audio_processing/utility/ooura_fft.h"
+#include "rtc_base/constructormagic.h"
+
+namespace webrtc {
+
+class ApmDataDumper;
+class AudioBuffer;
+
+class SignalClassifier {
+ public:
+  enum class SignalType { kHighlyNonStationary, kNonStationary, kStationary };
+
+  explicit SignalClassifier(ApmDataDumper* data_dumper);
+  ~SignalClassifier();
+
+  void Initialize(int sample_rate_hz);
+  void Analyze(const AudioBuffer& audio, SignalType* signal_type);
+
+ private:
+  class FrameExtender {
+   public:
+    FrameExtender(size_t frame_size, size_t extended_frame_size);
+    ~FrameExtender();
+
+    void ExtendFrame(rtc::ArrayView<const float> x,
+                     rtc::ArrayView<float> x_extended);
+
+   private:
+    std::vector<float> x_old_;
+
+    RTC_DISALLOW_IMPLICIT_CONSTRUCTORS(FrameExtender);
+  };
+
+  ApmDataDumper* const data_dumper_;
+  DownSampler down_sampler_;
+  std::unique_ptr<FrameExtender> frame_extender_;
+  NoiseSpectrumEstimator noise_spectrum_estimator_;
+  int sample_rate_hz_;
+  int initialization_frames_left_;
+  int consistent_classification_counter_;
+  SignalType last_signal_type_;
+  const OouraFft ooura_fft_;
+  RTC_DISALLOW_IMPLICIT_CONSTRUCTORS(SignalClassifier);
+};
+
+}  // namespace webrtc
+
+#endif  // MODULES_AUDIO_PROCESSING_LEVEL_CONTROLLER_SIGNAL_CLASSIFIER_H_
diff --git a/modules/audio_processing/test/aec_dump_based_simulator.cc b/modules/audio_processing/test/aec_dump_based_simulator.cc
index 83e8531..6d0b07c 100644
--- a/modules/audio_processing/test/aec_dump_based_simulator.cc
+++ b/modules/audio_processing/test/aec_dump_based_simulator.cc
@@ -473,6 +473,10 @@
           new RefinedAdaptiveFilter(*settings_.use_refined_adaptive_filter));
     }
 
+    if (settings_.use_lc) {
+      apm_config.level_controller.enabled = *settings_.use_lc;
+    }
+
     if (settings_.use_ed) {
       apm_config.residual_echo_detector.enabled = *settings_.use_ed;
     }
diff --git a/modules/audio_processing/test/audio_processing_simulator.cc b/modules/audio_processing/test/audio_processing_simulator.cc
index b4c3525..82bffe4 100644
--- a/modules/audio_processing/test/audio_processing_simulator.cc
+++ b/modules/audio_processing/test/audio_processing_simulator.cc
@@ -328,6 +328,9 @@
   if (settings_.use_aec3 && *settings_.use_aec3) {
     echo_control_factory.reset(new EchoCanceller3Factory());
   }
+  if (settings_.use_lc) {
+    apm_config.level_controller.enabled = *settings_.use_lc;
+  }
   if (settings_.use_hpf) {
     apm_config.high_pass_filter.enabled = *settings_.use_hpf;
   }
diff --git a/modules/audio_processing/test/audio_processing_simulator.h b/modules/audio_processing/test/audio_processing_simulator.h
index a6bdb90..41a3f45 100644
--- a/modules/audio_processing/test/audio_processing_simulator.h
+++ b/modules/audio_processing/test/audio_processing_simulator.h
@@ -66,6 +66,7 @@
   rtc::Optional<bool> use_extended_filter;
   rtc::Optional<bool> use_drift_compensation;
   rtc::Optional<bool> use_aec3;
+  rtc::Optional<bool> use_lc;
   rtc::Optional<bool> use_experimental_agc;
   rtc::Optional<int> aecm_routing_mode;
   rtc::Optional<bool> use_aecm_comfort_noise;
diff --git a/modules/audio_processing/test/audioproc_float.cc b/modules/audio_processing/test/audioproc_float.cc
index 554d6b4..c5229a4 100644
--- a/modules/audio_processing/test/audioproc_float.cc
+++ b/modules/audio_processing/test/audioproc_float.cc
@@ -121,6 +121,9 @@
 DEFINE_int(aec3,
            kParameterNotSpecifiedValue,
            "Activate (1) or deactivate(0) the experimental AEC mode AEC3");
+DEFINE_int(lc,
+           kParameterNotSpecifiedValue,
+           "Activate (1) or deactivate(0) the level control");
 DEFINE_int(experimental_agc,
            kParameterNotSpecifiedValue,
            "Activate (1) or deactivate(0) the experimental AGC");
@@ -258,6 +261,7 @@
                       &settings.use_refined_adaptive_filter);
 
   SetSettingIfFlagSet(FLAG_aec3, &settings.use_aec3);
+  SetSettingIfFlagSet(FLAG_lc, &settings.use_lc);
   SetSettingIfFlagSet(FLAG_experimental_agc, &settings.use_experimental_agc);
   SetSettingIfSpecified(FLAG_aecm_routing_mode, &settings.aecm_routing_mode);
   SetSettingIfFlagSet(FLAG_aecm_comfort_noise,
diff --git a/modules/audio_processing/test/debug_dump_test.cc b/modules/audio_processing/test/debug_dump_test.cc
index 4d3be48..56f47b0 100644
--- a/modules/audio_processing/test/debug_dump_test.cc
+++ b/modules/audio_processing/test/debug_dump_test.cc
@@ -484,6 +484,31 @@
   }
 }
 
+TEST_F(DebugDumpTest, VerifyLevelControllerExperimentalString) {
+  Config config;
+  AudioProcessing::Config apm_config;
+  apm_config.level_controller.enabled = true;
+  DebugDumpGenerator generator(config, apm_config);
+  generator.StartRecording();
+  generator.Process(100);
+  generator.StopRecording();
+
+  DebugDumpReplayer debug_dump_replayer_;
+
+  ASSERT_TRUE(debug_dump_replayer_.SetDumpFile(generator.dump_file_name()));
+
+  while (const rtc::Optional<audioproc::Event> event =
+             debug_dump_replayer_.GetNextEvent()) {
+    debug_dump_replayer_.RunNextEvent();
+    if (event->type() == audioproc::Event::CONFIG) {
+      const audioproc::Config* msg = &event->config();
+      ASSERT_TRUE(msg->has_experiments_description());
+      EXPECT_PRED_FORMAT2(testing::IsSubstring, "LevelController",
+                          msg->experiments_description().c_str());
+    }
+  }
+}
+
 TEST_F(DebugDumpTest, VerifyAgcClippingLevelExperimentalString) {
   Config config;
   // Arbitrarily set clipping gain to 17, which will never be the default.