forked from bartvdbraak/blender
73 lines
2.1 KiB
C++
73 lines
2.1 KiB
C++
/*
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* ***** BEGIN GPL LICENSE BLOCK *****
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*
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* Copyright 2009-2011 Jörg Hermann Müller
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*
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* This file is part of AudaSpace.
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*
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* Audaspace is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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*
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* AudaSpace is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with Audaspace; if not, write to the Free Software Foundation,
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* Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
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*
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* ***** END GPL LICENSE BLOCK *****
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*/
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/** \file audaspace/FX/AUD_ButterworthFactory.cpp
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* \ingroup audfx
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*/
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#include "AUD_ButterworthFactory.h"
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#include "AUD_IIRFilterReader.h"
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#include <cmath>
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#ifndef M_PI
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#define M_PI 3.14159265358979323846
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#endif
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#define BWPB41 0.76536686473
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#define BWPB42 1.84775906502
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AUD_ButterworthFactory::AUD_ButterworthFactory(AUD_Reference<AUD_IFactory> factory,
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float frequency) :
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AUD_DynamicIIRFilterFactory(factory),
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m_frequency(frequency)
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{
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}
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void AUD_ButterworthFactory::recalculateCoefficients(AUD_SampleRate rate,
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std::vector<float> &b,
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std::vector<float> &a)
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{
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float omega = 2 * tan(m_frequency * M_PI / rate);
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float o2 = omega * omega;
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float o4 = o2 * o2;
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float x1 = o2 + 2 * BWPB41 * omega + 4;
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float x2 = o2 + 2 * BWPB42 * omega + 4;
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float y1 = o2 - 2 * BWPB41 * omega + 4;
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float y2 = o2 - 2 * BWPB42 * omega + 4;
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float o228 = 2 * o2 - 8;
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float norm = x1 * x2;
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a.push_back(1);
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a.push_back((x1 + x2) * o228 / norm);
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a.push_back((x1 * y2 + x2 * y1 + o228 * o228) / norm);
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a.push_back((y1 + y2) * o228 / norm);
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a.push_back(y1 * y2 / norm);
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b.push_back(o4 / norm);
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b.push_back(4 * o4 / norm);
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b.push_back(6 * o4 / norm);
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b.push_back(b[1]);
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b.push_back(b[0]);
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}
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