biquad.h

/*
* Copyright (C) 2016 - 2024 Judd Niemann - All Rights Reserved.
* You may use, distribute and modify this code under the
* terms of the GNU Lesser General Public License, version 2.1
*
* You should have received a copy of GNU Lesser General Public License v2.1
* with this file. If not, please refer to: https://github.com/jniemann66/ReSampler
*/

#ifndef biquad_H
#define biquad_H

// Simple IIR biquad filter implementation

namespace ReSampler {

template<typename FloatType> class Biquad
{
public:

	// Naming conventions for coefficients are as follows:
	// numerator/input coeffs:			a0,a1,a2
	// denominator/feedback coeffs:		b1,b2
    // also, subtraction is performed on denominator coefficients,
    // so you must ensure the signs of the denominator coefficients are correct for subtraction.

	Biquad() = default;

	Biquad(FloatType a0, FloatType a1, FloatType a2, FloatType b1, FloatType b2)
		: a0(a0), a1(a1), a2(a2), b1(b1), b2(b2)
	{
	}

    FloatType filter(FloatType inSample)
    {
		// Biquad calculation using transposed Direct Form 2:
		FloatType outSample = inSample * a0 + z1;
		z1 = inSample * a1 + z2 - b1 * outSample;
		z2 = inSample * a2 - b2 * outSample;
		return outSample;
	}

    void setCoeffs(FloatType a0, FloatType a1, FloatType a2, FloatType b1, FloatType b2)
    {
		Biquad::a0 = a0;
		Biquad::a1 = a1;
		Biquad::a2 = a2;
		Biquad::b1 = b1;
		Biquad::b2 = b2;
	}

    void reset()
    {
		z1 = 0.0;
		z2 = 0.0;
	}

protected:
	FloatType a0{}, a1{}, a2{}, b1{}, b2{};
	double z1{0.0}, z2{0.0};
};

} // namespace ReSampler

#endif // biquad_H