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