AUD_HighpassFactory.cpp

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/*
 * $Id: AUD_HighpassFactory.cpp 35141 2011-02-25 10:21:56Z jesterking $
 *
 * ***** 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 *****
 */

#include "AUD_HighpassFactory.h"
#include "AUD_IIRFilterReader.h"

#include <cmath>

#ifndef M_PI
#define M_PI 3.14159265358979323846
#endif

AUD_HighpassFactory::AUD_HighpassFactory(AUD_IFactory* factory, float frequency,
                                                                                 float Q) :
                AUD_EffectFactory(factory),
                m_frequency(frequency),
                m_Q(Q)
{
}

AUD_IReader* AUD_HighpassFactory::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);
}