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/* -*- c-basic-offset: 4 indent-tabs-mode: nil -*- vi:set ts=8 sts=4 sw=4: */
/*
QM DSP library
Centre for Digital Music, Queen Mary, University of London.
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. See the file
COPYING included with this distribution for more information.
*/
#include "KaiserWindow.h"
#include "maths/MathUtilities.h"
KaiserWindow::Parameters
KaiserWindow::parametersForTransitionWidth(double attenuation,
double transition)
{
Parameters p;
p.length = 1 + (attenuation > 21.0 ?
ceil((attenuation - 7.95) / (2.285 * transition)) :
ceil(5.79 / transition));
p.beta = (attenuation > 50.0 ?
0.1102 * (attenuation - 8.7) :
attenuation > 21.0 ?
0.5842 * pow(attenuation - 21.0, 0.4) + 0.07886 * (attenuation - 21.0) :
0);
return p;
}
static double besselTerm(double x, int i)
{
if (i == 0) {
return 1;
} else {
double f = MathUtilities::factorial(i);
return pow(x/2, i*2) / (f*f);
}
}
static double bessel0(double x)
{
double b = 0.0;
for (int i = 0; i < 20; ++i) {
b += besselTerm(x, i);
}
return b;
}
void
KaiserWindow::init()
{
double denominator = bessel0(m_beta);
bool even = (m_length % 2 == 0);
for (int i = 0; i < (even ? m_length/2 : (m_length+1)/2); ++i) {
double k = double(2*i) / double(m_length-1) - 1.0;
m_window.push_back(bessel0(m_beta * sqrt(1.0 - k*k)) / denominator);
}
for (int i = 0; i < (even ? m_length/2 : (m_length-1)/2); ++i) {
m_window.push_back(m_window[int(m_length/2) - i - 1]);
}
}
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