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1 /* -*- c-basic-offset: 4 indent-tabs-mode: nil -*- vi:set ts=8 sts=4 sw=4: */
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2 /*
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3 Constant-Q library
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4 Copyright (c) 2013-2014 Queen Mary, University of London
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5
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6 Permission is hereby granted, free of charge, to any person
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7 obtaining a copy of this software and associated documentation
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8 files (the "Software"), to deal in the Software without
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9 restriction, including without limitation the rights to use, copy,
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10 modify, merge, publish, distribute, sublicense, and/or sell copies
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11 of the Software, and to permit persons to whom the Software is
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12 furnished to do so, subject to the following conditions:
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13
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14 The above copyright notice and this permission notice shall be
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15 included in all copies or substantial portions of the Software.
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16
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17 THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
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18 EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
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19 MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
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20 NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
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21 CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF
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22 CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
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23 WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
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24
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25 Except as contained in this notice, the names of the Centre for
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26 Digital Music; Queen Mary, University of London; and Chris Cannam
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27 shall not be used in advertising or otherwise to promote the sale,
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28 use or other dealings in this Software without prior written
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29 authorization.
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30 */
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31
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32 #include "KaiserWindow.h"
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33
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34 #include "MathUtilities.h"
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35
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36 KaiserWindow::Parameters
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37 KaiserWindow::parametersForTransitionWidth(double attenuation,
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38 double transition)
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39 {
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40 Parameters p;
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41 p.length = 1 + (attenuation > 21.0 ?
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42 ceil((attenuation - 7.95) / (2.285 * transition)) :
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43 ceil(5.79 / transition));
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44 p.beta = (attenuation > 50.0 ?
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45 0.1102 * (attenuation - 8.7) :
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46 attenuation > 21.0 ?
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47 0.5842 * pow(attenuation - 21.0, 0.4) + 0.07886 * (attenuation - 21.0) :
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48 0);
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49 return p;
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50 }
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51
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52 static double besselTerm(double x, int i)
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53 {
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54 if (i == 0) {
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55 return 1;
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56 } else {
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57 double f = MathUtilities::factorial(i);
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58 return pow(x/2, i*2) / (f*f);
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59 }
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60 }
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61
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62 static double bessel0(double x)
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63 {
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64 double b = 0.0;
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65 for (int i = 0; i < 20; ++i) {
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66 b += besselTerm(x, i);
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67 }
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68 return b;
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69 }
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70
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71 void
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72 KaiserWindow::init()
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73 {
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74 double denominator = bessel0(m_beta);
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75 bool even = (m_length % 2 == 0);
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76 for (int i = 0; i < (even ? m_length/2 : (m_length+1)/2); ++i) {
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77 double k = double(2*i) / double(m_length-1) - 1.0;
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78 m_window.push_back(bessel0(m_beta * sqrt(1.0 - k*k)) / denominator);
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79 }
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80 for (int i = 0; i < (even ? m_length/2 : (m_length-1)/2); ++i) {
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81 m_window.push_back(m_window[int(m_length/2) - i - 1]);
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82 }
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83 }
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