LatFilt.h

Go to the documentation of this file.

/*
        LatFilt.h
        
        Copyright 2006 David Yeh <dtyeh@ccrma.stanford.edu>
        
        Lattice digital filter.
        Assumes order of b = order of a.
        Assumes a0 = 1.
 
*/
/*
        This program 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; either version 2
        of the License, or (at your option) any later version.
 
        This program 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, write to the Free Software
        Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA
        02111-1307, USA or point your web browser to http://www.gnu.org.
*/
 
#ifndef _DSP_LatFilt_H_
#define _DSP_LatFilt_H_
 
namespace DSP {
 
// ORDER is the highest power of s in the transfer function
template <int ORDER>
class LatFilt
{
        public:
                double vcoef[ORDER+1];
                double kcoef[ORDER];
                double state[ORDER];
                double y;
 
                // fade factors
                double vf[ORDER+1];
                double kf[ORDER];
 
                
                void reset() 
                        {
                                for (int i = 0; i < ORDER; i++) {
                                                state[i] = 0;   // zero state
                                                vf[i] = 1;      // reset fade factor
                                                kf[i] = 1;
                                }
                                vf[ORDER] = 1;
                                y = 0;
                        }
 
                void init (double fs)
                        {
                                reset();
                                clearcoefs();
                        }
 
                void clearcoefs() {
                                for (int i=0; i< ORDER; i++) {
                                                vcoef[i] = 0;
                                                kcoef[i] = 0;
                                }
                                vcoef[ORDER] = 0;
                }
 
                sample_t process (sample_t s) {
                                double tmp;
 
                                int i = ORDER-1;
                                tmp = -kcoef[i]*state[i] + s;
                                y = vcoef[i+1]*(state[i] + kcoef[i]*tmp);
                                                
                                for (i = ORDER-2; i >= 0; i--) {
                                                tmp = -kcoef[i]*state[i] + tmp;
                                                state[i+1] = kcoef[i]*tmp + state[i];
                                                y = y + vcoef[i+1]*state[i+1];
                                }
                                state[0] = tmp;
                                y = y + vcoef[0]*tmp;
 
                                return (sample_t) y;
                }
 
                inline void set_vi(double coef, int i) {
                                vcoef[i] = coef;
                }
 
                inline void set_ki(double coef, int i) {
                                kcoef[i] = coef;
                }
};
 
} /* namespace DSP */
 
#endif /* _DSP_LatFilt_H_ */