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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 "modules/audio_processing/agc2/limiter_db_gain_curve.h"
#include <cmath>
#include "common_audio/include/audio_util.h"
#include "modules/audio_processing/agc2/agc2_common.h"
#include "rtc_base/checks.h"
namespace webrtc {
namespace {
double ComputeKneeStart(double max_input_level_db,
double knee_smoothness_db,
double compression_ratio) {
RTC_CHECK_LT((compression_ratio - 1.0) * knee_smoothness_db /
(2.0 * compression_ratio),
max_input_level_db);
return -knee_smoothness_db / 2.0 -
max_input_level_db / (compression_ratio - 1.0);
}
std::array<double, 3> ComputeKneeRegionPolynomial(double knee_start_dbfs,
double knee_smoothness_db,
double compression_ratio) {
const double a = (1.0 - compression_ratio) /
(2.0 * knee_smoothness_db * compression_ratio);
const double b = 1.0 - 2.0 * a * knee_start_dbfs;
const double c = a * knee_start_dbfs * knee_start_dbfs;
return {{a, b, c}};
}
double ComputeLimiterD1(double max_input_level_db, double compression_ratio) {
return (std::pow(10.0, -max_input_level_db / (20.0 * compression_ratio)) *
(1.0 - compression_ratio) / compression_ratio) /
kMaxAbsFloatS16Value;
}
constexpr double ComputeLimiterD2(double compression_ratio) {
return (1.0 - 2.0 * compression_ratio) / compression_ratio;
}
double ComputeLimiterI2(double max_input_level_db,
double compression_ratio,
double gain_curve_limiter_i1) {
RTC_CHECK_NE(gain_curve_limiter_i1, 0.f);
return std::pow(10.0, -max_input_level_db / (20.0 * compression_ratio)) /
gain_curve_limiter_i1 /
std::pow(kMaxAbsFloatS16Value, gain_curve_limiter_i1 - 1);
}
} // namespace
LimiterDbGainCurve::LimiterDbGainCurve()
: max_input_level_linear_(DbfsToFloatS16(max_input_level_db_)),
knee_start_dbfs_(ComputeKneeStart(max_input_level_db_,
knee_smoothness_db_,
compression_ratio_)),
knee_start_linear_(DbfsToFloatS16(knee_start_dbfs_)),
limiter_start_dbfs_(knee_start_dbfs_ + knee_smoothness_db_),
limiter_start_linear_(DbfsToFloatS16(limiter_start_dbfs_)),
knee_region_polynomial_(ComputeKneeRegionPolynomial(knee_start_dbfs_,
knee_smoothness_db_,
compression_ratio_)),
gain_curve_limiter_d1_(
ComputeLimiterD1(max_input_level_db_, compression_ratio_)),
gain_curve_limiter_d2_(ComputeLimiterD2(compression_ratio_)),
gain_curve_limiter_i1_(1.0 / compression_ratio_),
gain_curve_limiter_i2_(ComputeLimiterI2(max_input_level_db_,
compression_ratio_,
gain_curve_limiter_i1_)) {
static_assert(knee_smoothness_db_ > 0.0f, "");
static_assert(compression_ratio_ > 1.0f, "");
RTC_CHECK_GE(max_input_level_db_, knee_start_dbfs_ + knee_smoothness_db_);
}
constexpr double LimiterDbGainCurve::max_input_level_db_;
constexpr double LimiterDbGainCurve::knee_smoothness_db_;
constexpr double LimiterDbGainCurve::compression_ratio_;
double LimiterDbGainCurve::GetOutputLevelDbfs(double input_level_dbfs) const {
if (input_level_dbfs < knee_start_dbfs_) {
return input_level_dbfs;
} else if (input_level_dbfs < limiter_start_dbfs_) {
return GetKneeRegionOutputLevelDbfs(input_level_dbfs);
}
return GetCompressorRegionOutputLevelDbfs(input_level_dbfs);
}
double LimiterDbGainCurve::GetGainLinear(double input_level_linear) const {
if (input_level_linear < knee_start_linear_) {
return 1.0;
}
return DbfsToFloatS16(
GetOutputLevelDbfs(FloatS16ToDbfs(input_level_linear))) /
input_level_linear;
}
// Computes the first derivative of GetGainLinear() in `x`.
double LimiterDbGainCurve::GetGainFirstDerivativeLinear(double x) const {
// Beyond-knee region only.
RTC_CHECK_GE(x, limiter_start_linear_ - 1e-7 * kMaxAbsFloatS16Value);
return gain_curve_limiter_d1_ *
std::pow(x / kMaxAbsFloatS16Value, gain_curve_limiter_d2_);
}
// Computes the integral of GetGainLinear() in the range [x0, x1].
double LimiterDbGainCurve::GetGainIntegralLinear(double x0, double x1) const {
RTC_CHECK_LE(x0, x1); // Valid interval.
RTC_CHECK_GE(x0, limiter_start_linear_); // Beyond-knee region only.
auto limiter_integral = [this](const double& x) {
return gain_curve_limiter_i2_ * std::pow(x, gain_curve_limiter_i1_);
};
return limiter_integral(x1) - limiter_integral(x0);
}
double LimiterDbGainCurve::GetKneeRegionOutputLevelDbfs(
double input_level_dbfs) const {
return knee_region_polynomial_[0] * input_level_dbfs * input_level_dbfs +
knee_region_polynomial_[1] * input_level_dbfs +
knee_region_polynomial_[2];
}
double LimiterDbGainCurve::GetCompressorRegionOutputLevelDbfs(
double input_level_dbfs) const {
return (input_level_dbfs - max_input_level_db_) / compression_ratio_;
}
} // namespace webrtc
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