1 files changed, 65 insertions, 0 deletions
diff --git a/libs/qm-dsp/base/KaiserWindow.cpp b/libs/qm-dsp/base/KaiserWindow.cpp
new file mode 100644
index 0000000000..4fe838e090
--- /dev/null
+++ b/libs/qm-dsp/base/KaiserWindow.cpp
@@ -0,0 +1,65 @@
+/* -*- 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]);
+    }
+}