1 files changed, 183 insertions, 0 deletions
diff --git a/third_party/libwebrtc/modules/audio_processing/agc2/saturation_protector.cc b/third_party/libwebrtc/modules/audio_processing/agc2/saturation_protector.cc
new file mode 100644
index 0000000000..961baf4cd3
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+++ b/third_party/libwebrtc/modules/audio_processing/agc2/saturation_protector.cc
@@ -0,0 +1,183 @@
+/*
+ *  Copyright (c) 2018 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/agc2/saturation_protector.h"
+
+#include <memory>
+
+#include "modules/audio_processing/agc2/agc2_common.h"
+#include "modules/audio_processing/agc2/saturation_protector_buffer.h"
+#include "modules/audio_processing/logging/apm_data_dumper.h"
+#include "rtc_base/checks.h"
+#include "rtc_base/numerics/safe_minmax.h"
+
+namespace webrtc {
+namespace {
+
+constexpr int kPeakEnveloperSuperFrameLengthMs = 400;
+constexpr float kMinMarginDb = 12.0f;
+constexpr float kMaxMarginDb = 25.0f;
+constexpr float kAttack = 0.9988493699365052f;
+constexpr float kDecay = 0.9997697679981565f;
+
+// Saturation protector state. Defined outside of `SaturationProtectorImpl` to
+// implement check-point and restore ops.
+struct SaturationProtectorState {
+  bool operator==(const SaturationProtectorState& s) const {
+    return headroom_db == s.headroom_db &&
+           peak_delay_buffer == s.peak_delay_buffer &&
+           max_peaks_dbfs == s.max_peaks_dbfs &&
+           time_since_push_ms == s.time_since_push_ms;
+  }
+  inline bool operator!=(const SaturationProtectorState& s) const {
+    return !(*this == s);
+  }
+
+  float headroom_db;
+  SaturationProtectorBuffer peak_delay_buffer;
+  float max_peaks_dbfs;
+  int time_since_push_ms;  // Time since the last ring buffer push operation.
+};
+
+// Resets the saturation protector state.
+void ResetSaturationProtectorState(float initial_headroom_db,
+                                   SaturationProtectorState& state) {
+  state.headroom_db = initial_headroom_db;
+  state.peak_delay_buffer.Reset();
+  state.max_peaks_dbfs = kMinLevelDbfs;
+  state.time_since_push_ms = 0;
+}
+
+// Updates `state` by analyzing the estimated speech level `speech_level_dbfs`
+// and the peak level `peak_dbfs` for an observed frame. `state` must not be
+// modified without calling this function.
+void UpdateSaturationProtectorState(float peak_dbfs,
+                                    float speech_level_dbfs,
+                                    SaturationProtectorState& state) {
+  // Get the max peak over `kPeakEnveloperSuperFrameLengthMs` ms.
+  state.max_peaks_dbfs = std::max(state.max_peaks_dbfs, peak_dbfs);
+  state.time_since_push_ms += kFrameDurationMs;
+  if (rtc::SafeGt(state.time_since_push_ms, kPeakEnveloperSuperFrameLengthMs)) {
+    // Push `max_peaks_dbfs` back into the ring buffer.
+    state.peak_delay_buffer.PushBack(state.max_peaks_dbfs);
+    // Reset.
+    state.max_peaks_dbfs = kMinLevelDbfs;
+    state.time_since_push_ms = 0;
+  }
+
+  // Update the headroom by comparing the estimated speech level and the delayed
+  // max speech peak.
+  const float delayed_peak_dbfs =
+      state.peak_delay_buffer.Front().value_or(state.max_peaks_dbfs);
+  const float difference_db = delayed_peak_dbfs - speech_level_dbfs;
+  if (difference_db > state.headroom_db) {
+    // Attack.
+    state.headroom_db =
+        state.headroom_db * kAttack + difference_db * (1.0f - kAttack);
+  } else {
+    // Decay.
+    state.headroom_db =
+        state.headroom_db * kDecay + difference_db * (1.0f - kDecay);
+  }
+
+  state.headroom_db =
+      rtc::SafeClamp<float>(state.headroom_db, kMinMarginDb, kMaxMarginDb);
+}
+
+// Saturation protector which recommends a headroom based on the recent peaks.
+class SaturationProtectorImpl : public SaturationProtector {
+ public:
+  explicit SaturationProtectorImpl(float initial_headroom_db,
+                                   int adjacent_speech_frames_threshold,
+                                   ApmDataDumper* apm_data_dumper)
+      : apm_data_dumper_(apm_data_dumper),
+        initial_headroom_db_(initial_headroom_db),
+        adjacent_speech_frames_threshold_(adjacent_speech_frames_threshold) {
+    Reset();
+  }
+  SaturationProtectorImpl(const SaturationProtectorImpl&) = delete;
+  SaturationProtectorImpl& operator=(const SaturationProtectorImpl&) = delete;
+  ~SaturationProtectorImpl() = default;
+
+  float HeadroomDb() override { return headroom_db_; }
+
+  void Analyze(float speech_probability,
+               float peak_dbfs,
+               float speech_level_dbfs) override {
+    if (speech_probability < kVadConfidenceThreshold) {
+      // Not a speech frame.
+      if (adjacent_speech_frames_threshold_ > 1) {
+        // When two or more adjacent speech frames are required in order to
+        // update the state, we need to decide whether to discard or confirm the
+        // updates based on the speech sequence length.
+        if (num_adjacent_speech_frames_ >= adjacent_speech_frames_threshold_) {
+          // First non-speech frame after a long enough sequence of speech
+          // frames. Update the reliable state.
+          reliable_state_ = preliminary_state_;
+        } else if (num_adjacent_speech_frames_ > 0) {
+          // First non-speech frame after a too short sequence of speech frames.
+          // Reset to the last reliable state.
+          preliminary_state_ = reliable_state_;
+        }
+      }
+      num_adjacent_speech_frames_ = 0;
+    } else {
+      // Speech frame observed.
+      num_adjacent_speech_frames_++;
+
+      // Update preliminary level estimate.
+      UpdateSaturationProtectorState(peak_dbfs, speech_level_dbfs,
+                                     preliminary_state_);
+
+      if (num_adjacent_speech_frames_ >= adjacent_speech_frames_threshold_) {
+        // `preliminary_state_` is now reliable. Update the headroom.
+        headroom_db_ = preliminary_state_.headroom_db;
+      }
+    }
+    DumpDebugData();
+  }
+
+  void Reset() override {
+    num_adjacent_speech_frames_ = 0;
+    headroom_db_ = initial_headroom_db_;
+    ResetSaturationProtectorState(initial_headroom_db_, preliminary_state_);
+    ResetSaturationProtectorState(initial_headroom_db_, reliable_state_);
+  }
+
+ private:
+  void DumpDebugData() {
+    apm_data_dumper_->DumpRaw(
+        "agc2_saturation_protector_preliminary_max_peak_dbfs",
+        preliminary_state_.max_peaks_dbfs);
+    apm_data_dumper_->DumpRaw(
+        "agc2_saturation_protector_reliable_max_peak_dbfs",
+        reliable_state_.max_peaks_dbfs);
+  }
+
+  ApmDataDumper* const apm_data_dumper_;
+  const float initial_headroom_db_;
+  const int adjacent_speech_frames_threshold_;
+  int num_adjacent_speech_frames_;
+  float headroom_db_;
+  SaturationProtectorState preliminary_state_;
+  SaturationProtectorState reliable_state_;
+};
+
+}  // namespace
+
+std::unique_ptr<SaturationProtector> CreateSaturationProtector(
+    float initial_headroom_db,
+    int adjacent_speech_frames_threshold,
+    ApmDataDumper* apm_data_dumper) {
+  return std::make_unique<SaturationProtectorImpl>(
+      initial_headroom_db, adjacent_speech_frames_threshold, apm_data_dumper);
+}
+
+}  // namespace webrtc