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Limiter has been renamed to LimiterDbGainCurve, which is a more correct name and will allow in a follow-up CL to reuse the Limiter name for GainCurveApplier. This is done to allow to use the limiter without instancing the fixed digital gain controller and then to fix an AGC2 issue (namely, fixed gain applied after the adaptive one). Bug: webrtc:7494 Change-Id: Icd7050e3e51b832bfbf35e5cc61109215c5b1ca6 Reviewed-on: https://webrtc-review.googlesource.com/c/106901 Commit-Queue: Alessio Bazzica <alessiob@webrtc.org> Reviewed-by: Alex Loiko <aleloi@webrtc.org> Cr-Commit-Position: refs/heads/master@{#25322}
76 lines
3 KiB
C++
76 lines
3 KiB
C++
/*
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* Copyright (c) 2018 The WebRTC project authors. All Rights Reserved.
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*
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* Use of this source code is governed by a BSD-style license
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* that can be found in the LICENSE file in the root of the source
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* tree. An additional intellectual property rights grant can be found
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* in the file PATENTS. All contributing project authors may
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* be found in the AUTHORS file in the root of the source tree.
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*/
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#ifndef MODULES_AUDIO_PROCESSING_AGC2_LIMITER_DB_GAIN_CURVE_H_
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#define MODULES_AUDIO_PROCESSING_AGC2_LIMITER_DB_GAIN_CURVE_H_
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#include <array>
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#include "modules/audio_processing/agc2/agc2_testing_common.h"
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namespace webrtc {
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// A class for computing a limiter gain curve (in dB scale) given a set of
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// hard-coded parameters (namely, kLimiterDbGainCurveMaxInputLevelDbFs,
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// kLimiterDbGainCurveKneeSmoothnessDb, and
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// kLimiterDbGainCurveCompressionRatio). The generated curve consists of four
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// regions: identity (linear), knee (quadratic polynomial), compression
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// (linear), saturation (linear). The aforementioned constants are used to shape
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// the different regions.
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class LimiterDbGainCurve {
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public:
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LimiterDbGainCurve();
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double max_input_level_db() const { return max_input_level_db_; }
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double max_input_level_linear() const { return max_input_level_linear_; }
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double knee_start_linear() const { return knee_start_linear_; }
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double limiter_start_linear() const { return limiter_start_linear_; }
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// These methods can be marked 'constexpr' in C++ 14.
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double GetOutputLevelDbfs(double input_level_dbfs) const;
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double GetGainLinear(double input_level_linear) const;
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double GetGainFirstDerivativeLinear(double x) const;
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double GetGainIntegralLinear(double x0, double x1) const;
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private:
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double GetKneeRegionOutputLevelDbfs(double input_level_dbfs) const;
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double GetCompressorRegionOutputLevelDbfs(double input_level_dbfs) const;
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static constexpr double max_input_level_db_ = test::kLimiterMaxInputLevelDbFs;
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static constexpr double knee_smoothness_db_ = test::kLimiterKneeSmoothnessDb;
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static constexpr double compression_ratio_ = test::kLimiterCompressionRatio;
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const double max_input_level_linear_;
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// Do not modify signal with level <= knee_start_dbfs_.
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const double knee_start_dbfs_;
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const double knee_start_linear_;
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// The upper end of the knee region, which is between knee_start_dbfs_ and
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// limiter_start_dbfs_.
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const double limiter_start_dbfs_;
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const double limiter_start_linear_;
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// Coefficients {a, b, c} of the knee region polynomial
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// ax^2 + bx + c in the DB scale.
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const std::array<double, 3> knee_region_polynomial_;
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// Parameters for the computation of the first derivative of GetGainLinear().
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const double gain_curve_limiter_d1_;
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const double gain_curve_limiter_d2_;
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// Parameters for the computation of the integral of GetGainLinear().
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const double gain_curve_limiter_i1_;
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const double gain_curve_limiter_i2_;
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};
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} // namespace webrtc
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#endif // MODULES_AUDIO_PROCESSING_AGC2_LIMITER_DB_GAIN_CURVE_H_
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