NodeVCFMoogLP.hpp

/*
 * Klang – a node+text-based synthesizer library
 *
 * This file is part of the *wellen* library (https://github.com/dennisppaul/wellen).
 * Copyright (c) 2022 Dennis P Paul.
 *
 * This library is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, version 3.
 *
 * This library is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
 * General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program. If not, see <http://www.gnu.org/licenses/>.
 */


/**
 *       [ NODE_VCF_MOOG_LP    ]
 *       +---------------------+
 *       |                     |
 * IN00--| SIGNAL       SIGNAL |--OUT00
 * IN01--| CUTOFF              |
 * IN02--| RESONANCE           |
 *       |                     |
 *       +---------------------+
 */

#ifndef NodeVCFMoogLP_hpp
#define NodeVCFMoogLP_hpp

#include "NodeVCF.hpp"

namespace klang {
    class NodeVCFMoogLP : public NodeVCF {
        /*
         Notes :
         in[x] and out[x] are member variables, init to 0.0 the controls:
         
         fc = cutoff, nearly linear [0,1] -> [0, fs/2]
         res = resonance [0, 4] -> [no resonance, self-oscillation]
         
         Code :
         Tfloat MoogVCF::run(float input, float fc, float res)
         {
         float f = fc * 1.16;
         float fb = res * (1.0 - 0.15 * f * f);
         input -= out4 * fb;
         input *= 0.35013 * (f*f)*(f*f);
         out1 = input + 0.3 * in1 + (1 - f) * out1; // Pole 1
         in1  = input;
         out2 = out1 + 0.3 * in2 + (1 - f) * out2;  // Pole 2
         in2  = out1;
         out3 = out2 + 0.3 * in3 + (1 - f) * out3;  // Pole 3
         in3  = out2;
         out4 = out3 + 0.3 * in4 + (1 - f) * out4;  // Pole 4
         in4  = out3;
         return out4;
         }
         
         from https://www.musicdsp.org/en/latest/Filters/26-moog-vcf-variation-2.html
         */

        void set_command(KLANG_CMD_TYPE pCommand, KLANG_CMD_TYPE* pPayLoad) {
            switch (pCommand) {
                case KLANG_SET_CUTOFF_F32:
                    set_cutoff(KlangMath::FLOAT_32(pPayLoad));
                    break;
                case KLANG_SET_RESONANCE_F32:
                    set_resonance(KlangMath::FLOAT_32(pPayLoad));
                    break;
            }
        }

    protected:
        float out1 = 0;
        float out2 = 0;
        float out3 = 0;
        float out4 = 0;
        float in1  = 0;
        float in2  = 0;
        float in3  = 0;
        float in4  = 0;

        float process(float input) {
            // fc  = cutoff, nearly linear [0,1] -> [0, fs/2]
            // res = resonance [0, 1] -> [no resonance, self-oscillation]
            const float f  = mCutoff * 1.16f;
            const float fb = (mResonance * 4) * (1.0f - 0.15f * f * f);
            input -= out4 * fb;
            input *= 0.35013f * (f * f) * (f * f);
            out1 = input + 0.3f * in1 + (1.0f - f) * out1;  // Pole 1
            in1  = input;
            out2 = out1 + 0.3f * in2 + (1.0f - f) * out2;  // Pole 2
            in2  = out1;
            out3 = out2 + 0.3f * in3 + (1.0f - f) * out3;  // Pole 3
            in3  = out2;
            out4 = out3 + 0.3f * in4 + (1.0f - f) * out4;  // Pole 4
            in4  = out3;
            //    return out4;
            if (out4 != out4) {
                out1 = 0;
                out2 = 0;
                out3 = 0;
                out4 = 0;
                in1  = 0;
                in2  = 0;
                in3  = 0;
                in4  = 0;
                return 0;
            } else {
                return out4 > SIGNAL_MAX ? SIGNAL_MAX : (out4 < SIGNAL_MIN ? SIGNAL_MIN : out4);
            }
        }
    };
}  // namespace klang
#endif /* NodeVCFMoogLP_hpp */