TDFII.h

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/*
        TDFII.h
        
        Copyright 2006-7
                David Yeh <dtyeh@ccrma.stanford.edu> (implementation)
                Tim Goetze <tim@quitte.de> (cosmetics)
 
        transposed Direct Form II 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_TDFII_H_
#define _DSP_TDFII_H_
 
namespace DSP {
 
// ORDER is the highest power of s in the transfer function
template <int Order>
class TDFII
{
        public:
                double a[Order + 1];
                double b[Order + 1];
                double h[Order + 1];
        
                void reset() 
                        {
                                for (int i = 0; i <= Order; ++i)
                                        h[i] = 0;   // zero state
                        }
 
                void init (double fs)
                        {
                                reset();
                                clear();
                        }
 
                void clear() 
                        {
                                for (int i=0; i<= Order; i++) 
                                                a[i] = b[i] = 1;
                        }
 
                /* per-band recursion:
                 *      y = 2 * (a * (x - x[-2]) + c * y[-1] - b * y[-2]) 
                 */
                sample_t process (sample_t s)
                        {
                                double y = h[0] + b[0] * s;
 
                                for (int i = 1; i < Order; ++i) 
                                                h[i - 1] = h[i] + b[i] * s - a[i] * y;
 
                                h[Order - 1] = b[Order] * s - a[Order] * y;
 
                                return (sample_t) y;
                        }
};
 
} /* namespace DSP */
 
#endif /* _DSP_TDFII_H_ */