andrewm@0: /*
andrewm@0:   TouchKeys: multi-touch musical keyboard control software
andrewm@0:   Copyright (c) 2013 Andrew McPherson
andrewm@0: 
andrewm@0:   This program is free software: you can redistribute it and/or modify
andrewm@0:   it under the terms of the GNU General Public License as published by
andrewm@0:   the Free Software Foundation, either version 3 of the License, or
andrewm@0:   (at your option) any later version.
andrewm@0:  
andrewm@0:   This program is distributed in the hope that it will be useful,
andrewm@0:   but WITHOUT ANY WARRANTY; without even the implied warranty of
andrewm@0:   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
andrewm@0:   GNU General Public License for more details.
andrewm@0: 
andrewm@0:   You should have received a copy of the GNU General Public License
andrewm@0:   along with this program.  If not, see <http://www.gnu.org/licenses/>.
andrewm@0:  
andrewm@0:   =====================================================================
andrewm@0: 
andrewm@0:   IIRFilter.cpp: template class handling an Nth-order IIR filter on data
andrewm@0:   in a given Node.
andrewm@0: */
andrewm@0: 
andrewm@20: #ifdef _MSC_VER
andrewm@20: #define _USE_MATH_DEFINES
andrewm@20: #endif
andrewm@20: #include <cmath>
andrewm@0: #include "IIRFilter.h"
andrewm@0: 
andrewm@0: // These are static functions to design IIR filters specifically for floating-point datatypes.
andrewm@0: // vector<double> and be converted to another type at the end if needed.
andrewm@0: 
andrewm@0: void designFirstOrderLowpass(std::vector<double>& bCoeffs, std::vector<double>& aCoeffs,
andrewm@0:                                     double cutoffFrequency, double sampleFrequency) {
andrewm@0:     bCoeffs.clear();
andrewm@0:     aCoeffs.clear();
andrewm@0:     
andrewm@0:     double omega = tan(M_PI * cutoffFrequency / sampleFrequency);
andrewm@0:     double n = 1.0 / (1.0 + omega);
andrewm@0:     
andrewm@0:     bCoeffs.push_back(omega * n);       // B0
andrewm@0:     bCoeffs.push_back(omega * n);       // B1
andrewm@0:     aCoeffs.push_back((omega - 1) * n); // A1
andrewm@0: }
andrewm@0: 
andrewm@0: void designFirstOrderHighpass(std::vector<double>& bCoeffs, std::vector<double>& aCoeffs,
andrewm@0:                              double cutoffFrequency, double sampleFrequency) {
andrewm@0:     bCoeffs.clear();
andrewm@0:     aCoeffs.clear();
andrewm@0:     
andrewm@0:     double omega = tan(M_PI * cutoffFrequency / sampleFrequency);
andrewm@0:     double n = 1.0 / (1.0 + omega);
andrewm@0:     
andrewm@0:     bCoeffs.push_back(n);               // B0
andrewm@0:     bCoeffs.push_back(-n);              // B1
andrewm@0:     aCoeffs.push_back((omega - 1) * n); // A1
andrewm@0: }
andrewm@0: 
andrewm@0: void designSecondOrderLowpass(std::vector<double>& bCoeffs, std::vector<double>& aCoeffs,
andrewm@0:                              double cutoffFrequency, double q, double sampleFrequency) {
andrewm@0:     bCoeffs.clear();
andrewm@0:     aCoeffs.clear();
andrewm@0:     
andrewm@0:     double omega = tan(M_PI * cutoffFrequency / sampleFrequency);
andrewm@0:     double n = 1.0 / (omega*omega + omega/q + 1.0);
andrewm@0:     double b0 = n * omega * omega;
andrewm@0:     
andrewm@0:     bCoeffs.push_back(b0);       // B0
andrewm@0:     bCoeffs.push_back(2.0 * b0); // B1
andrewm@0:     bCoeffs.push_back(b0);       // B2
andrewm@0:     aCoeffs.push_back(2.0 * n * (omega * omega - 1.0));   // A1
andrewm@0:     aCoeffs.push_back(n * (omega * omega - omega / q + 1.0));
andrewm@0: }
andrewm@0: 
andrewm@0: void designSecondOrderHighpass(std::vector<double>& bCoeffs, std::vector<double>& aCoeffs,
andrewm@0:                               double cutoffFrequency, double q, double sampleFrequency) {
andrewm@0:     bCoeffs.clear();
andrewm@0:     aCoeffs.clear();
andrewm@0:     
andrewm@0:     double omega = tan(M_PI * cutoffFrequency / sampleFrequency);
andrewm@0:     double n = 1.0 / (omega*omega + omega/q + 1.0);
andrewm@0:     
andrewm@0:     bCoeffs.push_back(n);        // B0
andrewm@0:     bCoeffs.push_back(-2.0 * n); // B1
andrewm@0:     bCoeffs.push_back(n);        // B2
andrewm@0:     aCoeffs.push_back(2.0 * n * (omega * omega - 1.0));   // A1
andrewm@0:     aCoeffs.push_back(n * (omega * omega - omega / q + 1.0));
andrewm@0: }
andrewm@0: 
andrewm@0: void designSecondOrderBandpass(std::vector<double>& bCoeffs, std::vector<double>& aCoeffs,
andrewm@0:                                double cutoffFrequency, double q, double sampleFrequency) {
andrewm@0:     bCoeffs.clear();
andrewm@0:     aCoeffs.clear();
andrewm@0:     
andrewm@0:     double omega = tan(M_PI * cutoffFrequency / sampleFrequency);
andrewm@0:     double n = 1.0 / (omega*omega + omega/q + 1.0);
andrewm@0:     double b0 = n * omega / q;
andrewm@0:     bCoeffs.push_back(b0);       // B0
andrewm@0:     bCoeffs.push_back(0.0);      // B1
andrewm@0:     bCoeffs.push_back(-b0);      // B2
andrewm@0:     aCoeffs.push_back(2.0 * n * (omega * omega - 1.0));   // A1
andrewm@0:     aCoeffs.push_back(n * (omega * omega - omega / q + 1.0));
andrewm@0: }