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* 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 <array>
#include "modules/audio_processing/agc2/agc2_testing_common.h"
namespace webrtc {
// A class for computing a limiter gain curve (in dB scale) given a set of
// hard-coded parameters (namely, kLimiterDbGainCurveMaxInputLevelDbFs,
// kLimiterDbGainCurveKneeSmoothnessDb, and
// kLimiterDbGainCurveCompressionRatio). The generated curve consists of four
// regions: identity (linear), knee (quadratic polynomial), compression
// (linear), saturation (linear). The aforementioned constants are used to shape
// the different regions.
class LimiterDbGainCurve {
double max_input_level_db() const { return max_input_level_db_; }
double max_input_level_linear() const { return max_input_level_linear_; }
double knee_start_linear() const { return knee_start_linear_; }
double limiter_start_linear() const { return limiter_start_linear_; }
// These methods can be marked 'constexpr' in C++ 14.
double GetOutputLevelDbfs(double input_level_dbfs) const;
double GetGainLinear(double input_level_linear) const;
double GetGainFirstDerivativeLinear(double x) const;
double GetGainIntegralLinear(double x0, double x1) const;
double GetKneeRegionOutputLevelDbfs(double input_level_dbfs) const;
double GetCompressorRegionOutputLevelDbfs(double input_level_dbfs) const;
static constexpr double max_input_level_db_ = test::kLimiterMaxInputLevelDbFs;
static constexpr double knee_smoothness_db_ = test::kLimiterKneeSmoothnessDb;
static constexpr double compression_ratio_ = test::kLimiterCompressionRatio;
const double max_input_level_linear_;
// Do not modify signal with level <= knee_start_dbfs_.
const double knee_start_dbfs_;
const double knee_start_linear_;
// The upper end of the knee region, which is between knee_start_dbfs_ and
// limiter_start_dbfs_.
const double limiter_start_dbfs_;
const double limiter_start_linear_;
// Coefficients {a, b, c} of the knee region polynomial
// ax^2 + bx + c in the DB scale.
const std::array<double, 3> knee_region_polynomial_;
// Parameters for the computation of the first derivative of GetGainLinear().
const double gain_curve_limiter_d1_;
const double gain_curve_limiter_d2_;
// Parameters for the computation of the integral of GetGainLinear().
const double gain_curve_limiter_i1_;
const double gain_curve_limiter_i2_;
} // namespace webrtc