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      1 /*
      2  * Copyright (C) 2013 The Android Open Source Project
      3  *
      4  * Licensed under the Apache License, Version 2.0 (the "License");
      5  * you may not use this file except in compliance with the License.
      6  * You may obtain a copy of the License at
      7  *
      8  *      http://www.apache.org/licenses/LICENSE-2.0
      9  *
     10  * Unless required by applicable law or agreed to in writing, software
     11  * distributed under the License is distributed on an "AS IS" BASIS,
     12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     13  * See the License for the specific language governing permissions and
     14  * limitations under the License.
     15  */
     16 //#define LOG_NDEBUG 0
     17 
     18 #include <cmath>
     19 
     20 #include "common/core/math.h"
     21 #include "common/core/types.h"
     22 #include "dsp/core/basic.h"
     23 #include "dsp/core/interpolation.h"
     24 #include "dsp/core/dynamic_range_compression.h"
     25 
     26 #include <android/log.h>
     27 
     28 namespace le_fx {
     29 
     30 // Definitions for static const class members declared in
     31 // dynamic_range_compression.h.
     32 const float AdaptiveDynamicRangeCompression::kMinAbsValue = 0.000001f;
     33 const float AdaptiveDynamicRangeCompression::kMinLogAbsValue =
     34     0.032766999999999997517097227728299912996590137481689453125f;
     35 const float AdaptiveDynamicRangeCompression::kFixedPointLimit = 32767.0f;
     36 const float AdaptiveDynamicRangeCompression::kInverseFixedPointLimit =
     37     1.0f / AdaptiveDynamicRangeCompression::kFixedPointLimit;
     38 const float AdaptiveDynamicRangeCompression::kDefaultKneeThresholdInDecibel =
     39     -8.0f;
     40 const float AdaptiveDynamicRangeCompression::kCompressionRatio = 7.0f;
     41 const float AdaptiveDynamicRangeCompression::kTauAttack = 0.001f;
     42 const float AdaptiveDynamicRangeCompression::kTauRelease = 0.015f;
     43 
     44 AdaptiveDynamicRangeCompression::AdaptiveDynamicRangeCompression() {
     45   static const float kTargetGain[] = {
     46       1.0f, 2.0f, 3.0f, 4.0f, 5.0f };
     47   static const float kKneeThreshold[] = {
     48       -8.0f, -8.0f, -8.5f, -9.0f, -10.0f };
     49   target_gain_to_knee_threshold_.Initialize(
     50       &kTargetGain[0], &kKneeThreshold[0],
     51       sizeof(kTargetGain) / sizeof(kTargetGain[0]));
     52 }
     53 
     54 bool AdaptiveDynamicRangeCompression::Initialize(
     55         float target_gain, float sampling_rate) {
     56   set_knee_threshold_via_target_gain(target_gain);
     57   sampling_rate_ = sampling_rate;
     58   state_ = 0.0f;
     59   compressor_gain_ = 1.0f;
     60   if (kTauAttack > 0.0f) {
     61     const float taufs = kTauAttack * sampling_rate_;
     62     alpha_attack_ = std::exp(-1.0f / taufs);
     63   } else {
     64     alpha_attack_ = 0.0f;
     65   }
     66   if (kTauRelease > 0.0f) {
     67     const float taufs = kTauRelease * sampling_rate_;
     68     alpha_release_ = std::exp(-1.0f / taufs);
     69   } else {
     70     alpha_release_ = 0.0f;
     71   }
     72   // Feed-forward topology
     73   slope_ = 1.0f / kCompressionRatio - 1.0f;
     74   return true;
     75 }
     76 
     77 float AdaptiveDynamicRangeCompression::Compress(float x) {
     78   const float max_abs_x = std::max(std::fabs(x), kMinLogAbsValue);
     79   const float max_abs_x_dB = math::fast_log(max_abs_x);
     80   // Subtract Threshold from log-encoded input to get the amount of overshoot
     81   const float overshoot = max_abs_x_dB - knee_threshold_;
     82   // Hard half-wave rectifier
     83   const float rect = std::max(overshoot, 0.0f);
     84   // Multiply rectified overshoot with slope
     85   const float cv = rect * slope_;
     86   const float prev_state = state_;
     87   if (cv <= state_) {
     88     state_ = alpha_attack_ * state_ + (1.0f - alpha_attack_) * cv;
     89   } else {
     90     state_ = alpha_release_ * state_ + (1.0f - alpha_release_) * cv;
     91   }
     92   compressor_gain_ *=
     93       math::ExpApproximationViaTaylorExpansionOrder5(state_ - prev_state);
     94   x *= compressor_gain_;
     95   if (x > kFixedPointLimit) {
     96     return kFixedPointLimit;
     97   }
     98   if (x < -kFixedPointLimit) {
     99     return -kFixedPointLimit;
    100   }
    101   return x;
    102 }
    103 
    104 void AdaptiveDynamicRangeCompression::Compress(float *x1, float *x2) {
    105   // Taking the maximum amplitude of both channels
    106   const float max_abs_x = std::max(std::fabs(*x1),
    107     std::max(std::fabs(*x2), kMinLogAbsValue));
    108   const float max_abs_x_dB = math::fast_log(max_abs_x);
    109   // Subtract Threshold from log-encoded input to get the amount of overshoot
    110   const float overshoot = max_abs_x_dB - knee_threshold_;
    111   // Hard half-wave rectifier
    112   const float rect = std::max(overshoot, 0.0f);
    113   // Multiply rectified overshoot with slope
    114   const float cv = rect * slope_;
    115   const float prev_state = state_;
    116   if (cv <= state_) {
    117     state_ = alpha_attack_ * state_ + (1.0f - alpha_attack_) * cv;
    118   } else {
    119     state_ = alpha_release_ * state_ + (1.0f - alpha_release_) * cv;
    120   }
    121   compressor_gain_ *=
    122       math::ExpApproximationViaTaylorExpansionOrder5(state_ - prev_state);
    123   *x1 *= compressor_gain_;
    124   if (*x1 > kFixedPointLimit) {
    125     *x1 = kFixedPointLimit;
    126   }
    127   if (*x1 < -kFixedPointLimit) {
    128     *x1 = -kFixedPointLimit;
    129   }
    130   *x2 *= compressor_gain_;
    131   if (*x2 > kFixedPointLimit) {
    132     *x2 = kFixedPointLimit;
    133   }
    134   if (*x2 < -kFixedPointLimit) {
    135     *x2 = -kFixedPointLimit;
    136   }
    137 }
    138 
    139 }  // namespace le_fx
    140 
    141