TapDelayPitchShifter.h

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// Copyright Epic Games, Inc. All Rights Reserved.
 
#pragma once
 
#include "CoreMinimal.h"
#include "DSP/Dsp.h"
#include "DSP/Delay.h"
 
namespace Audio
{
    // Class which reads doppler-shifted tap from a delay buffer 
    class FTapDelayPitchShifter
    {
    public:
        static constexpr float MinDelayLength = 10.0f;
        static constexpr float MaxDelayLength = 100.0f;
        static constexpr float MaxAbsPitchShiftInOctaves = 6.0f;
        
        // Constructor
        SIGNALPROCESSING_API FTapDelayPitchShifter();
 
        // Virtual Destructor
        SIGNALPROCESSING_API virtual ~FTapDelayPitchShifter();
 
        // Initialization of the internal delay with given sample rate, pitch shift in semitones, and delay length in milliseconds
        SIGNALPROCESSING_API void Init(const float InSampleRate, const float InPitchShift, const float InDelayLength);
 
        // Sets the internal delay line length.
        SIGNALPROCESSING_API void SetDelayLength(const float InDelayLength);
 
        // Sets the pitch shift in semitones
        SIGNALPROCESSING_API void SetPitchShift(const float InPitchScaleSemitones);
 
        // Sets the pitch shift in terms of a sample rate ratio
        SIGNALPROCESSING_API void SetPitchShiftRatio(const float InPitchShiftRatio);
        
        // Reads the next sample tap from the input delay buffer
        SIGNALPROCESSING_API float ReadDopplerShiftedTapFromDelay(const Audio::FDelay& InDelayBuffer, const float ReadOffsetMilliseconds = 0.0f);
 
        // Process whole block of audio reading to and writing from delay line from input buffer
        SIGNALPROCESSING_API void ProcessAudio(Audio::FDelay& InDelayBuffer, const float* InAudioBuffer, const int32 InNumFrames, float* OutAudioBuffer);
        
    private:
        SIGNALPROCESSING_API void UpdatePhasorPhaseIncrement();
        
        float SampleRate = 0.0f;
        Audio::FExponentialEase CurrentDelayLength;
        float CurrentTargetDelayLength = 0.0f;
        float CurrentPitchShift = 0.0f;
        float CurrentPitchShiftRatio = 1.0f;
        float PhasorPhase = 0.0f;
        float PhasorPhaseIncrement = 0.0f;
    };
 
}