DynamicDelayAPF.h

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// Copyright Epic Games, Inc. All Rights Reserved.
 
#pragma once
 
#include "CoreMinimal.h"
#include "IntegerDelay.h"
#include "BufferVectorOperations.h"
#include "AllPassFractionalDelay.h"
#include "LinearInterpFractionalDelay.h"
 
namespace Audio
{
    // All Pass Filter with a long fractional delay which can be set per a sample. This filter is specifically designed for 
    // reverb applications where filter delay lines are long.
    class FDynamicDelayAPF
    {
    public:
        // InG is the filter coefficient used in the long delay all pass filter.
        // InMinDelay is the minimum allowable delay of the all pass filter.
        // InMaxDelay is the maximum allowable delay of the all pass filter.
        // InMaxNumInternalBufferSamples is the maximum internal block size used internally. 
        // InSampleRate is the current rendering sample rate. Used to convert parameter ease time from seconds to samples.
        SIGNALPROCESSING_API FDynamicDelayAPF(float InG, int32 InMinDelay, int32 InMaxDelay, int32 InMaxNumInternalBufferSamples, float InSampleRate);
 
        // Destructor
        SIGNALPROCESSING_API ~FDynamicDelayAPF();
 
        // Set the APF feedback/feedforward gain coefficient
        void SetG(float InG)
        {
            G.SetValue(InG, EaseTimeInSec);
        }
 
        // Processes InSamples through the all pass filter and populates OutSamples with the filter output.
        // InDelays denotes the per-sample delay of the allpass. It must have an equal number of elements as InSamples
        SIGNALPROCESSING_API void ProcessAudio(const FAlignedFloatBuffer& InSamples, const FAlignedFloatBuffer& InDelays, FAlignedFloatBuffer& OutSamples);
 
        // Zeros the internal delay line.
        SIGNALPROCESSING_API void Reset();
 
        void SetEaseTimeInSec(float InEaseTimeInSec) { EaseTimeInSec = InEaseTimeInSec; }
 
    protected:
 
        // Process one block of audio.
        SIGNALPROCESSING_API void ProcessAudioBlock(const float* InSamples, const FAlignedFloatBuffer& InFractionalDelays, const int32 InNum, float* OutSamples);
 
    private:
        // Feedback/Feedforward gain coefficient
        FLinearEase G;
        float EaseTimeInSec;
        int32 MinDelay;
        int32 MaxDelay;
        int32 NumDelaySamples;
        int32 NumInternalBufferSamples;
 
        // Buffers for block processing
        FAlignedFloatBuffer FractionalDelays;
        FAlignedFloatBuffer DelayLineInput;
        FAlignedFloatBuffer WorkBufferA;
        FAlignedFloatBuffer WorkBufferB;
 
        // Delay line memory.
        TUniquePtr<FAlignedBlockBuffer> IntegerDelayLine;
        TUniquePtr<FLinearInterpFractionalDelay> FractionalDelayLine;
    };
 
}