Biquad.h

// This code is based on the code credited below, but it has been modified further
//
//  Biquad.h
//
//  Created by Nigel Redmon on 11/24/12
//  EarLevel Engineering: earlevel.com
//  Copyright 2012 Nigel Redmon
//
//  For a complete explanation of the Biquad code:
//  http://www.earlevel.com/main/2012/11/25/biquad-c-source-code/
//
//  License:
//
//  This source code is provided as is, without warranty.
//  You may copy and distribute verbatim copies of this document.
//  You may modify and use this source code to create binary code
//  for your own purposes, free or commercial.
//

#pragma once

class Biquad {
        public:
                typedef enum
                {
                        lowpass,
                        highpass,
                        bandpass,
                        notch,
                        peak,
                        lowshelf,
                        highshelf
                } Type;
                struct Settings {
                        double fs; 
                        Type type; 
                        double cutoff; 
                        double q; 
                        double peakGainDb; 
                };
                Biquad();
                Biquad(const Settings& settings);
                ~Biquad();
                int setup(const Settings& settings);

                float process(float in);

                void clean();

                void setType(Type type);
                void setQ(double Q);
                void setFc(double Fc);
                void setPeakGain(double peakGainDB);

                Type getType();
                double getQ();
                double getFc();
                double getPeakGain();

                double getStartingQ();
                double getStartingFc();
                double getStartingPeakGain();

        protected:
                void calcBiquad(void);

                Type type;
                double a0, a1, a2, b1, b2;
                double Fc, Q, peakGain;
                double Fs;
                double startFc, startQ, startPeakGain;
                double z1, z2;
};

inline float Biquad::process(float in) {
        double out = in * a0 + z1;
        z1 = in * a1 + z2 - b1 * out;
        z2 = in * a2 - b2 * out;
        return out;
}