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/*
dsp/windows.h
Copyright 2004 Tim Goetze <tim@quitte.de>
http://quitte.de/dsp/
select few common windowing algorithms.
*/
/*
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_WINDOWS_H_
#define _DSP_WINDOWS_H_
namespace DSP {
/* prototypes for window value application ... */
typedef void (*window_sample_func_t) (d_sample &, d_sample);
/* ... which go as template parameters for the window calculation below */
inline void
store_sample (d_sample & d, d_sample s)
{
d = s;
}
inline void
apply_window (d_sample &d, d_sample s)
{
d *= s;
}
template <window_sample_func_t F>
void
hanning (d_sample * s, int n)
{
/* TODO: speed up by using DSP::Sine */
for (int i = 0; i < n; ++i)
{
register double f = (double) i / n - 1;
F (s[i], .5 - .5 * cos (2 * M_PI * f));
}
}
template <window_sample_func_t F>
void
blackman (d_sample * s, int n)
{
register float w = n;
for (int i = 0; i < n; ++i)
{
register float f = (float) i;
register double b = .42f -
.5f * cos (2.f * f * M_PI / w) +
.08 * cos (4.f * f * M_PI / w);
F (s[i], b);
}
}
template <window_sample_func_t F>
void
blackman_harris (d_sample * s, int n)
{
register double w1 = 2.f * M_PI / (n - 1);
register double w2 = 2.f * w1;
register double w3 = 3.f * w1;
for (int i = 0; i < n; ++i)
{
register double f = (double) i;
register double bh = .35875f -
.48829f * cos (w1 * f) +
.14128f * cos (w2 * f) -
.01168f * cos (w3 * f);
bh *= .761f;
F (s[i], bh);
}
}
/* helper for the kaiser window, courtesy of R. Dobson, courtesy of csound */
inline double
besseli (double x)
{
double ax, ans;
double y;
if ((ax = fabs (x)) < 3.75)
{
y = x / 3.75;
y *= y;
ans = (1.0 + y * (3.5156229 +
y * (3.0899424 +
y * (1.2067492 +
y * (0.2659732 +
y * (0.360768e-1 +
y * 0.45813e-2))))));
}
else
{
y = 3.75 / ax;
ans = ((exp (ax) / sqrt (ax))
* (0.39894228 +
y * (0.1328592e-1 +
y * (0.225319e-2 +
y * (-0.157565e-2 +
y * (0.916281e-2 +
y * (-0.2057706e-1 +
y * (0.2635537e-1 +
y * (-0.1647633e-1 +
y * 0.392377e-2)))))))));
}
return ans;
}
template <window_sample_func_t F>
void
kaiser (d_sample * s, int n, double beta)
{
double bb = besseli (beta);
int si = 0;
for (double i = -n / 2 + .1; si < n; ++si, ++i)
{
double k = besseli ((beta * sqrt (1 - pow ((2 * i / (n - 1)), 2)))) / bb;
/* can you spell hack */
if (!finite (k))
k = 0;
F (s[si], k);
}
/* assymetrical hack: sort out first value!
win[0] = win[len-1];
*/
}
}; /* namespace DSP */
#endif /* _DSP_WINDOWS_H_ */
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