blender/intern/audaspace/FX/AUD_LowpassFactory.cpp

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/*
* $Id$
*
* ***** BEGIN LGPL LICENSE BLOCK *****
*
* Copyright 2009 Jörg Hermann Müller
*
* This file is part of AudaSpace.
*
* AudaSpace is free software: you can redistribute it and/or modify
* it under the terms of the GNU Lesser General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* AudaSpace is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public License
* along with AudaSpace. If not, see <http://www.gnu.org/licenses/>.
*
* ***** END LGPL LICENSE BLOCK *****
*/
#include "AUD_LowpassFactory.h"
#include "AUD_IIRFilterReader.h"
#include <cmath>
#ifndef M_PI
#define M_PI 3.14159265358979323846
#endif
AUD_LowpassFactory::AUD_LowpassFactory(AUD_IFactory* factory, float frequency,
float Q) :
AUD_EffectFactory(factory),
m_frequency(frequency),
m_Q(Q)
{
}
AUD_IReader* AUD_LowpassFactory::createReader() const
{
AUD_IReader* reader = getReader();
// calculate coefficients
float w0 = 2 * M_PI * m_frequency / reader->getSpecs().rate;
float alpha = sin(w0) / (2 * m_Q);
float norm = 1 + alpha;
float c = cos(w0);
std::vector<float> a, b;
a.push_back(1);
a.push_back(-2 * c / norm);
a.push_back((1 - alpha) / norm);
b.push_back((1 - c) / (2 * norm));
b.push_back((1 - c) / norm);
b.push_back(b[0]);
return new AUD_IIRFilterReader(reader, b, a);
}