67 lines
1.8 KiB
Plaintext
67 lines
1.8 KiB
Plaintext
/*
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* This file is part of libsidplayfp, a SID player engine.
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*
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* Copyright 2011-2016 Leandro Nini <drfiemost@users.sourceforge.net>
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* Copyright 2007-2010 Antti Lankila
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* Copyright 2004 Dag Lem <resid@nimrod.no>
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*
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* This program 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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* This program 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 this program; if not, write to the Free Software
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* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
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*/
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#define EXTERNALFILTER_CPP
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#include "ExternalFilter.h"
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namespace reSIDfp
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{
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/**
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* Get the 3 dB attenuation point.
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*
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* @param res the resistance value in Ohms
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* @param cap the capacitance value in Farads
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*/
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inline double getW0(double res, double cap)
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{
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return 1. / (res * cap);
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}
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ExternalFilter::ExternalFilter() :
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Vlp(0),
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Vhp(0),
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w0lp_1_s7(0),
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w0hp_1_s17(0)
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{
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reset();
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}
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void ExternalFilter::setClockFrequency(double frequency)
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{
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// Low-pass: R = 10kOhm, C = 1000pF; w0l = 1/RC = 1/(1e4*1e-9) = 100000
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w0lp_1_s7 = static_cast<int>(getW0(10e3, 1000e-12) / frequency * (1 << 7) + 0.5);
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// High-pass: R = 1kOhm, C = 10uF; w0h = 1/RC = 1/(1e3*1e-5) = 100
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w0hp_1_s17 = static_cast<int>(getW0(1e3, 10e-6) / frequency * (1 << 17) + 0.5);
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}
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void ExternalFilter::reset()
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{
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// State of filter.
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Vlp = 0; //1 << (15 + 11);
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Vhp = 0;
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}
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} // namespace reSIDfp
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