LongDelayAPF.h

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// Copyright Epic Games, Inc. All Rights Reserved.
 
#pragma once
 
#include "CoreMinimal.h"
#include "DSP/BufferVectorOperations.h"
#include "DSP/AlignedBlockBuffer.h"
 
namespace Audio
{
    // All Pass Filter with a long delay. This filter is specifically designed for 
    // reverb applications where filter delay lines are long.
    class FLongDelayAPF
    {
    public:
        // InG is the filter coefficient used in the long delay all pass filter.
        // InNumDelaySamples is the delay line length in samples.
        // InMaxNumInternalBufferSamples is the maximum internal block size used internally. 
        SIGNALPROCESSING_API FLongDelayAPF(float InG, int32 InNumDelaySamples, int32 InMaxNumInternalBufferSamples);
 
        // Destructor
        SIGNALPROCESSING_API ~FLongDelayAPF();
 
        // Set the APF feedback/feedforward gain coefficient
        void SetG(float InG) { G = InG; }
 
        // Process InSamples and place filtered data in OutSamples
        SIGNALPROCESSING_API void ProcessAudio(const FAlignedFloatBuffer& InSamples, FAlignedFloatBuffer& OutSamples);
 
        // Process Samples in place
        SIGNALPROCESSING_API void ProcessAudio(FAlignedFloatBuffer& Samples);
 
        // Process InSamples and place filtered data in OutSamples and delay line samples in OutDelaySamples.
        // The OutDelaySamples correspond to "w[n] = InSamples[n] + InG * w[n - InDelay]"
        SIGNALPROCESSING_API void ProcessAudio(const FAlignedFloatBuffer& InSamples, FAlignedFloatBuffer& OutSamples, FAlignedFloatBuffer& OutDelaySamples);
 
        // Sets delay line values to zero.
        SIGNALPROCESSING_API void Reset();
 
    private:
        // Performs all pass filtering on an audio block of BlockSize samples are less. 
        // InNum must be less than or equal to BlockSize.
        SIGNALPROCESSING_API void ProcessAudioBlock(const float* InSamples, const float* InDelaySamples, const int32 InNum, float* OutSamples, float* OutDelaySamples);
 
        SIGNALPROCESSING_API int32 GetNumInternalBufferSamples() const;
 
        // Feedback/Feedforward gain coefficient
        float G;
 
        // Delay in samples
        int32 NumDelaySamples;
 
        // Buffer size for internal block processing.
        int32 NumInternalBufferSamples;
 
        // Buffer for block operations.
        FAlignedFloatBuffer WorkBuffer;
 
        // Filter delay line memory.
        TUniquePtr<FAlignedBlockBuffer> DelayLine;
    };
 
}