BiQuadFilter.h

Go to the documentation of this file.

// Copyright Epic Games, Inc. All Rights Reserved.
 
#pragma once
 
#include "CoreMinimal.h"
#include "DSP/Dsp.h"
 
namespace Audio
{
    // Simple biquad filter structure handling a biquad formulation
    // See: https://en.wikipedia.org/wiki/Digital_biquad_filter
    // Calculations of coefficients are handled outside this class.
    // Filter coefficients are public and are intended to be used externally.
    class UE_DEPRECATED(5.5, "Audio::FBiquad is deprecated in favor of Audio::FBiquadFilter due to performance issues") FBiquad
    {
    public:
        FBiquad()
            : A0(1.0f)
            , A1(0.0f)
            , A2(0.0f)
            , B1(0.0f)
            , B2(0.0f)
        {
            Reset();
        }
 
        inline float ProcessAudio(const float InSample)
        {
            // Use the biquad difference eq: y(n) = a0*x(n) + a1*x(n-1) + a2*x(n-2) - b1*y(n-1) - b2*y(n-2) 
            const float Output = A0 * InSample + A1 * X_Z1 + A2 * X_Z2 - B1 * Y_Z1 - B2 * Y_Z2;
 
            // Apply the z-transforms
            Y_Z2 = Y_Z1;
            Y_Z1 = Output;
 
            X_Z2 = X_Z1;
            X_Z1 = InSample;
 
            return Output;
        }
 
        // Reset the filter (flush delays)
        void Reset()
        {
            X_Z1 = 0.0f;
            X_Z2 = 0.0f;
            Y_Z1 = 0.0f;
            Y_Z2 = 0.0f;
        }
 
    public:
        // Biquad filter coefficients
        float A0;
        float A1;
        float A2;
        float B1;
        float B2;
 
    protected:
        float X_Z1; // previous inputs z-transforms
        float X_Z2;
        float Y_Z1; // prvious outputs z-transforms
        float Y_Z2;
    };
}