EQ.h

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// Copyright Epic Games, Inc. All Rights Reserved.
 
#pragma once
 
#include "CoreMinimal.h"
#include "DSP/Filter.h"
 
namespace Audio
{
    // Equalizer filter
    // An equalizer is a cascaded (serial) band of parametric EQs
    // This filter allows for setting each band with variable Bandwidth/Q, Frequency, and Gain
    class FEqualizer
    {
    public:
        // Constructor
        SIGNALPROCESSING_API FEqualizer();
 
        // Destructor
        SIGNALPROCESSING_API ~FEqualizer();
 
        // Initialize the equalizer
        SIGNALPROCESSING_API void Init(const float InSampleRate, const int32 InNumBands, const int32 InNumChannels);
 
        // Sets whether or not the band is enabled
        SIGNALPROCESSING_API void SetBandEnabled(const int32 InBand, const bool bEnabled);
 
        // Sets all params of the band at once
        SIGNALPROCESSING_API void SetBandParams(const int32 InBand, const float InFrequency, const float InBandwidth, const float InGainDB);
 
        // Sets the band frequency
        SIGNALPROCESSING_API void SetBandFrequency(const int32 InBand, const float InFrequency);
 
        // Sets the band resonance (use alternatively to bandwidth)
        SIGNALPROCESSING_API void SetBandBandwidth(const int32 InBand, const float InBandwidth);
 
        // Sets the band gain in decibels
        SIGNALPROCESSING_API void SetBandGainDB(const int32 InBand, const float InGainDB);
 
        // Processes the audio frame (audio frame must have channels equal to that used during initialization)
        SIGNALPROCESSING_API void ProcessAudioFrame(const float* InAudio, float* OutAudio);
 
    private:
 
        // The number of channels in the equalizer
        int32 NumChannels;
 
        // The array of biquad filters
        TArray<FBiquadFilter> FilterBands;
        
        // Temporary array for processing audio.
        TArray<float> WorkBuffer;
    };
 
}