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81 lines
1.8 KiB
C++
81 lines
1.8 KiB
C++
/*
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TDFII.h
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Copyright 2006-7
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David Yeh <dtyeh@ccrma.stanford.edu> (implementation)
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Tim Goetze <tim@quitte.de> (cosmetics)
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transposed Direct Form II digital filter.
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Assumes order of b = order of a.
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Assumes a0 = 1.
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*/
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/*
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This program is free software; you can redistribute it and/or
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modify it under the terms of the GNU General Public License
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as published by the Free Software Foundation; either version 2
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of the License, or (at your option) any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program; if not, write to the Free Software
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Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA
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02111-1307, USA or point your web browser to http://www.gnu.org.
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*/
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#ifndef _DSP_TDFII_H_
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#define _DSP_TDFII_H_
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namespace DSP {
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// ORDER is the highest power of s in the transfer function
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template <int Order>
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class TDFII
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{
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public:
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double a[Order + 1];
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double b[Order + 1];
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double h[Order + 1];
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void reset()
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{
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for (int i = 0; i <= Order; ++i)
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h[i] = 0; // zero state
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}
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void init (double fs)
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{
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reset();
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clear();
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}
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void clear()
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{
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for (int i=0; i<= Order; i++)
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a[i] = b[i] = 1;
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}
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/* per-band recursion:
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* y = 2 * (a * (x - x[-2]) + c * y[-1] - b * y[-2])
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*/
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sample_t process (sample_t s)
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{
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double y = h[0] + b[0] * s;
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for (int i = 1; i < Order; ++i)
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h[i - 1] = h[i] + b[i] * s - a[i] * y;
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h[Order - 1] = b[Order] * s - a[Order] * y;
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return (sample_t) y;
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}
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};
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} /* namespace DSP */
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#endif /* _DSP_TDFII_H_ */
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