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64 lines
2.2 KiB
64 lines
2.2 KiB
/*
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* Copyright 2022 The Android Open Source Project
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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#ifndef FLOWGRAPH_LIMITER_H
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#define FLOWGRAPH_LIMITER_H
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#include <atomic>
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#include <unistd.h>
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#include <sys/types.h>
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#include "FlowGraphNode.h"
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namespace FLOWGRAPH_OUTER_NAMESPACE::flowgraph {
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class Limiter : public FlowGraphFilter {
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public:
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explicit Limiter(int32_t channelCount);
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int32_t onProcess(int32_t numFrames) override;
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const char *getName() override {
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return "Limiter";
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}
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private:
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// These numbers are based on a polynomial spline for a quadratic solution Ax^2 + Bx + C
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// The range is up to 3 dB, (10^(3/20)), to match AudioTrack for float data.
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static constexpr float kPolynomialSplineA = -0.6035533905; // -(1+sqrt(2))/4
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static constexpr float kPolynomialSplineB = 2.2071067811; // (3+sqrt(2))/2
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static constexpr float kPolynomialSplineC = -0.6035533905; // -(1+sqrt(2))/4
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static constexpr float kXWhenYis3Decibels = 1.8284271247; // -1+2sqrt(2)
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/**
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* Process an input based on the following:
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* If between -1 and 1, return the input value.
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* If above kXWhenYis3Decibels, return sqrt(2).
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* If below -kXWhenYis3Decibels, return -sqrt(2).
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* If between 1 and kXWhenYis3Decibels, use a quadratic spline (Ax^2 + Bx + C).
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* If between -kXWhenYis3Decibels and -1, use the absolute value for the spline and flip it.
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* The derivative of the spline is 1 at 1 and 0 at kXWhenYis3Decibels.
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* This way, the graph is both continuous and differentiable.
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*/
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float processFloat(float in);
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// Use the previous valid output for NaN inputs
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float mLastValidOutput = 0.0f;
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};
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} /* namespace FLOWGRAPH_OUTER_NAMESPACE::flowgraph */
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#endif //FLOWGRAPH_LIMITER_H
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