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