Blender V2.61 - r43446

AUD_LowpassFactory.cpp

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00001 /*
00002  * ***** BEGIN GPL LICENSE BLOCK *****
00003  *
00004  * Copyright 2009-2011 Jörg Hermann Müller
00005  *
00006  * This file is part of AudaSpace.
00007  *
00008  * Audaspace is free software; you can redistribute it and/or modify
00009  * it under the terms of the GNU General Public License as published by
00010  * the Free Software Foundation; either version 2 of the License, or
00011  * (at your option) any later version.
00012  *
00013  * AudaSpace is distributed in the hope that it will be useful,
00014  * but WITHOUT ANY WARRANTY; without even the implied warranty of
00015  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
00016  * GNU General Public License for more details.
00017  *
00018  * You should have received a copy of the GNU General Public License
00019  * along with Audaspace; if not, write to the Free Software Foundation,
00020  * Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
00021  *
00022  * ***** END GPL LICENSE BLOCK *****
00023  */
00024 
00030 #include "AUD_LowpassFactory.h"
00031 #include "AUD_IIRFilterReader.h"
00032 
00033 #include <cmath>
00034 
00035 #ifndef M_PI
00036 #define M_PI 3.14159265358979323846
00037 #endif
00038 
00039 AUD_LowpassFactory::AUD_LowpassFactory(AUD_Reference<AUD_IFactory> factory, float frequency,
00040                                        float Q) :
00041         AUD_DynamicIIRFilterFactory(factory),
00042         m_frequency(frequency),
00043         m_Q(Q)
00044 {
00045 }
00046 
00047 void AUD_LowpassFactory::recalculateCoefficients(AUD_SampleRate rate,
00048                                                  std::vector<float> &b,
00049                                                  std::vector<float> &a)
00050 {
00051     float w0 = 2 * M_PI * m_frequency / rate;
00052     float alpha = sin(w0) / (2 * m_Q);
00053     float norm = 1 + alpha;
00054     float c = cos(w0);
00055     a.push_back(1);
00056     a.push_back(-2 * c / norm);
00057     a.push_back((1 - alpha) / norm);
00058     b.push_back((1 - c) / (2 * norm));
00059     b.push_back((1 - c) / norm);
00060     b.push_back(b[0]);
00061 }