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+/*
+ * Copyright (C) 2013 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+#ifndef LE_FX_ENGINE_DSP_CORE_DYNAMIC_RANGE_COMPRESSION_H_
+#define LE_FX_ENGINE_DSP_CORE_DYNAMIC_RANGE_COMPRESSION_H_
+
+#include "common/core/types.h"
+#include "common/core/math.h"
+#include "dsp/core/basic.h"
+#include "dsp/core/interpolation.h"
+
+//#define LOG_NDEBUG 0
+#include <cutils/log.h>
+
+
+namespace le_fx {
+
+// An adaptive dynamic range compression algorithm. The gain adaptation is made
+// at the logarithmic domain and it is based on a Branching-Smooth compensated
+// digital peak detector with different time constants for attack and release.
+class AdaptiveDynamicRangeCompression {
+ public:
+    AdaptiveDynamicRangeCompression();
+
+    // Initializes the compressor using prior information. It assumes that the
+    // input signal is speech from high-quality recordings that is scaled and then
+    // fed to the compressor. The compressor is tuned according to the target gain
+    // that is expected to be applied.
+    //
+    // Target gain receives values between 0.0 and 10.0. The knee threshold is
+    // reduced as the target gain increases in order to fit the increased range of
+    // values.
+    //
+    // Values between 1.0 and 2.0 will only mildly affect your signal. Higher
+    // values will reduce the dynamic range of the signal to the benefit of
+    // increased loudness.
+    //
+    // If nothing is known regarding the input, a `target_gain` of 1.0f is a
+    // relatively safe choice for many signals.
+    bool Initialize(float target_gain, float sampling_rate);
+
+  // A fast version of the algorithm that uses approximate computations for the
+  // log(.) and exp(.).
+  float Compress(float x);
+
+  // Stereo channel version of the compressor
+  void Compress(float *x1, float *x2);
+
+  // This version is slower than Compress(.) but faster than CompressSlow(.)
+  float CompressNormalSpeed(float x);
+
+  // A slow version of the algorithm that is easier for further developement,
+  // tuning and debugging
+  float CompressSlow(float x);
+
+  // Sets knee threshold (in decibel).
+  void set_knee_threshold(float decibel);
+
+  // Sets knee threshold via the target gain using an experimentally derived
+  // relationship.
+  void set_knee_threshold_via_target_gain(float target_gain);
+
+ private:
+  // The minimum accepted absolute input value and it's natural logarithm. This
+  // is to prevent numerical issues when the input is close to zero
+  static const float kMinAbsValue;
+  static const float kMinLogAbsValue;
+  // Fixed-point arithmetic limits
+  static const float kFixedPointLimit;
+  static const float kInverseFixedPointLimit;
+  // The default knee threshold in decibel. The knee threshold defines when the
+  // compressor is actually starting to compress the value of the input samples
+  static const float kDefaultKneeThresholdInDecibel;
+  // The compression ratio is the reciprocal of the slope of the line segment
+  // above the threshold (in the log-domain). The ratio controls the
+  // effectiveness of the compression.
+  static const float kCompressionRatio;
+  // The attack time of the envelope detector
+  static const float kTauAttack;
+  // The release time of the envelope detector
+  static const float kTauRelease;
+
+  float sampling_rate_;
+  // the internal state of the envelope detector
+  float state_;
+  // the latest gain factor that was applied to the input signal
+  float compressor_gain_;
+  // attack constant for exponential dumping
+  float alpha_attack_;
+  // release constant for exponential dumping
+  float alpha_release_;
+  float slope_;
+  // The knee threshold
+  float knee_threshold_;
+  float knee_threshold_in_decibel_;
+  // This interpolator provides the function that relates target gain to knee
+  // threshold.
+  sigmod::InterpolatorLinear<float> target_gain_to_knee_threshold_;
+
+  LE_FX_DISALLOW_COPY_AND_ASSIGN(AdaptiveDynamicRangeCompression);
+};
+
+}  // namespace le_fx
+
+#include "dsp/core/dynamic_range_compression-inl.h"
+
+#endif  // LE_FX_ENGINE_DSP_CORE_DYNAMIC_RANGE_COMPRESSION_H_