FoldbackDistortion.h

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// Copyright Epic Games, Inc. All Rights Reserved.
 
#pragma once
 
#include "CoreMinimal.h"
#include "DSP/Osc.h"
 
namespace Audio
{
    // Foldback distortion effect
    // https://en.wikipedia.org/wiki/Foldback_(power_supply_design)
    class FFoldbackDistortion
    {
    public:
        // Constructor
        SIGNALPROCESSING_API FFoldbackDistortion();
 
        // Destructor
        SIGNALPROCESSING_API ~FFoldbackDistortion();
 
        // Initialize the equalizer
        SIGNALPROCESSING_API void Init(const float InSampleRate, const int32 InNumChannels);
 
        // Sets the foldback distortion threshold
        SIGNALPROCESSING_API void SetThresholdDb(const float InThresholdDb);
 
        // Sets the input gain
        SIGNALPROCESSING_API void SetInputGainDb(const float InInputGainDb);
 
        // Sets the output gain
        SIGNALPROCESSING_API void SetOutputGainDb(const float InOutputGainDb);
 
        // Processes a single audio sample
        SIGNALPROCESSING_API float ProcessAudioSample(const float InSample);
 
        // Processes a mono stream
        SIGNALPROCESSING_API void ProcessAudioFrame(const float* InFrame, float* OutFrame);
 
        // Processes a stereo stream
        SIGNALPROCESSING_API void ProcessAudio(const float* InBuffer, const int32 InNumSamples, float* OutBuffer);
 
    private:
        // Threshold to check before folding audio back on itself
        float Threshold;
 
        // Threshold times 2
        float Threshold2;
 
        // Threshold time 4
        float Threshold4;
 
        // Input gain used to force hitting the threshold
        float InputGain;
 
        // A final gain scaler to apply to the output
        float OutputGain;
 
        // How many channels we expect the audio intput to be.
        int32 NumChannels;
    };
 
}