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/*
TDFII.h
Copyright 2006-7
David Yeh <dtyeh@ccrma.stanford.edu> (implementation)
2006-14
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 3
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 {
/* N is the highest power of s in the transfer function */
template <int N>
class TDFII
{
public:
double a[N+1];
double b[N+1];
double h[N+1];
void reset()
{
for (int i = 0; i <= N; ++i)
h[i] = 0; // zero state
}
void init (double fs)
{
reset();
clear();
}
void clear()
{
for (int i=0; i<= N; i++)
a[i] = b[i] = 0;
b[0] = 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<N; ++i)
h[i-1] = h[i] + b[i]*s - a[i]*y;
h[N-1] = b[N]*s - a[N]*y;
return (sample_t) y;
}
};
} /* namespace DSP */
#endif /* DSP_TDFII_H */
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