Chris@124: /* -*- c-basic-offset: 4 indent-tabs-mode: nil -*-  vi:set ts=8 sts=4 sw=4: */
Chris@124: 
Chris@124: /*
Chris@124:     QM DSP library
Chris@124:     Centre for Digital Music, Queen Mary, University of London.
Chris@124:  
Chris@124:     This program is free software; you can redistribute it and/or
Chris@124:     modify it under the terms of the GNU General Public License as
Chris@124:     published by the Free Software Foundation; either version 2 of the
Chris@124:     License, or (at your option) any later version.  See the file
Chris@124:     COPYING included with this distribution for more information.
Chris@124: */
Chris@124: 
Chris@124: #include "KaiserWindow.h"
Chris@124: 
Chris@124: #include "maths/MathUtilities.h"
Chris@124: 
Chris@124: KaiserWindow::Parameters
Chris@124: KaiserWindow::parametersForTransitionWidth(double attenuation,
Chris@124: 					   double transition)
Chris@124: {
Chris@124:     Parameters p;
Chris@124:     p.length = 1 + (attenuation > 21.0 ?
Chris@124: 		    ceil((attenuation - 7.95) / (2.285 * transition)) :
Chris@124: 		    ceil(5.79 / transition));
Chris@124:     p.beta = (attenuation > 50.0 ? 
Chris@124: 	      0.1102 * (attenuation - 8.7) :
Chris@124: 	      attenuation > 21.0 ? 
Chris@124: 	      0.5842 * pow(attenuation - 21.0, 0.4) + 0.07886 * (attenuation - 21.0) :
Chris@124: 	      0);
Chris@124:     return p;
Chris@124: }
Chris@124: 
Chris@124: static double besselTerm(double x, int i)
Chris@124: {
Chris@124:     if (i == 0) {
Chris@124: 	return 1;
Chris@124:     } else {
Chris@124: 	double f = MathUtilities::factorial(i);
Chris@124: 	return pow(x/2, i*2) / (f*f);
Chris@124:     }
Chris@124: }
Chris@124: 
Chris@124: static double bessel0(double x)
Chris@124: {
Chris@124:     double b = 0.0;
Chris@124:     for (int i = 0; i < 20; ++i) {
Chris@124: 	b += besselTerm(x, i);
Chris@124:     }
Chris@124:     return b;
Chris@124: }
Chris@124: 
Chris@124: void
Chris@124: KaiserWindow::init()
Chris@124: {
Chris@124:     double denominator = bessel0(m_beta);
Chris@124:     for (int i = 0; i < m_length; ++i) {
Chris@124: 	double k = double(2*i) / double(m_length-1) - 1.0;
Chris@124: 	m_window.push_back(bessel0(m_beta * sqrt(1.0 - k*k)) / denominator);
Chris@124:     }
Chris@124: }