blender/intern/audaspace/FX/AUD_ButterworthFactory.cpp

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/*
* ***** BEGIN GPL LICENSE BLOCK *****
*
* Copyright 2009-2011 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 General Public License as published by
* the Free Software Foundation; either version 2 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 General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with Audaspace; if not, write to the Free Software Foundation,
* Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
*
* ***** END GPL LICENSE BLOCK *****
*/
2011-02-25 10:21:56 +00:00
/** \file audaspace/FX/AUD_ButterworthFactory.cpp
* \ingroup audfx
*/
#include "AUD_ButterworthFactory.h"
#include "AUD_IIRFilterReader.h"
#include <cmath>
#ifndef M_PI
#define M_PI 3.14159265358979323846
#endif
#define BWPB41 0.76536686473
#define BWPB42 1.84775906502
AUD_ButterworthFactory::AUD_ButterworthFactory(AUD_Reference<AUD_IFactory> factory,
float frequency) :
AUD_DynamicIIRFilterFactory(factory),
m_frequency(frequency)
{
}
void AUD_ButterworthFactory::recalculateCoefficients(AUD_SampleRate rate,
std::vector<float> &b,
std::vector<float> &a)
{
float omega = 2 * tan(m_frequency * M_PI / rate);
float o2 = omega * omega;
float o4 = o2 * o2;
float x1 = o2 + 2 * BWPB41 * omega + 4;
float x2 = o2 + 2 * BWPB42 * omega + 4;
float y1 = o2 - 2 * BWPB41 * omega + 4;
float y2 = o2 - 2 * BWPB42 * omega + 4;
float o228 = 2 * o2 - 8;
float norm = x1 * x2;
a.push_back(1);
a.push_back((x1 + x2) * o228 / norm);
a.push_back((x1 * y2 + x2 * y1 + o228 * o228) / norm);
a.push_back((y1 + y2) * o228 / norm);
a.push_back(y1 * y2 / norm);
b.push_back(o4 / norm);
b.push_back(4 * o4 / norm);
b.push_back(6 * o4 / norm);
b.push_back(b[1]);
b.push_back(b[0]);
}