limiter_db_gain_curve.h (3021B)
1 /* 2 * Copyright (c) 2018 The WebRTC project authors. All Rights Reserved. 3 * 4 * Use of this source code is governed by a BSD-style license 5 * that can be found in the LICENSE file in the root of the source 6 * tree. An additional intellectual property rights grant can be found 7 * in the file PATENTS. All contributing project authors may 8 * be found in the AUTHORS file in the root of the source tree. 9 */ 10 11 #ifndef MODULES_AUDIO_PROCESSING_AGC2_LIMITER_DB_GAIN_CURVE_H_ 12 #define MODULES_AUDIO_PROCESSING_AGC2_LIMITER_DB_GAIN_CURVE_H_ 13 14 #include <array> 15 16 #include "modules/audio_processing/agc2/agc2_testing_common.h" 17 18 namespace webrtc { 19 20 // A class for computing a limiter gain curve (in dB scale) given a set of 21 // hard-coded parameters (namely, kLimiterDbGainCurveMaxInputLevelDbFs, 22 // kLimiterDbGainCurveKneeSmoothnessDb, and 23 // kLimiterDbGainCurveCompressionRatio). The generated curve consists of four 24 // regions: identity (linear), knee (quadratic polynomial), compression 25 // (linear), saturation (linear). The aforementioned constants are used to shape 26 // the different regions. 27 class LimiterDbGainCurve { 28 public: 29 LimiterDbGainCurve(); 30 31 double max_input_level_db() const { return max_input_level_db_; } 32 double max_input_level_linear() const { return max_input_level_linear_; } 33 double knee_start_linear() const { return knee_start_linear_; } 34 double limiter_start_linear() const { return limiter_start_linear_; } 35 36 // These methods can be marked 'constexpr' in C++ 14. 37 double GetOutputLevelDbfs(double input_level_dbfs) const; 38 double GetGainLinear(double input_level_linear) const; 39 double GetGainFirstDerivativeLinear(double x) const; 40 double GetGainIntegralLinear(double x0, double x1) const; 41 42 private: 43 double GetKneeRegionOutputLevelDbfs(double input_level_dbfs) const; 44 double GetCompressorRegionOutputLevelDbfs(double input_level_dbfs) const; 45 46 static constexpr double max_input_level_db_ = test::kLimiterMaxInputLevelDbFs; 47 static constexpr double knee_smoothness_db_ = test::kLimiterKneeSmoothnessDb; 48 static constexpr double compression_ratio_ = test::kLimiterCompressionRatio; 49 50 const double max_input_level_linear_; 51 52 // Do not modify signal with level <= knee_start_dbfs_. 53 const double knee_start_dbfs_; 54 const double knee_start_linear_; 55 56 // The upper end of the knee region, which is between knee_start_dbfs_ and 57 // limiter_start_dbfs_. 58 const double limiter_start_dbfs_; 59 const double limiter_start_linear_; 60 61 // Coefficients {a, b, c} of the knee region polynomial 62 // ax^2 + bx + c in the DB scale. 63 const std::array<double, 3> knee_region_polynomial_; 64 65 // Parameters for the computation of the first derivative of GetGainLinear(). 66 const double gain_curve_limiter_d1_; 67 const double gain_curve_limiter_d2_; 68 69 // Parameters for the computation of the integral of GetGainLinear(). 70 const double gain_curve_limiter_i1_; 71 const double gain_curve_limiter_i2_; 72 }; 73 74 } // namespace webrtc 75 76 #endif // MODULES_AUDIO_PROCESSING_AGC2_LIMITER_DB_GAIN_CURVE_H_