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Large Pack of OldSkool DOS MOD Trackers
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goattracker_2.68.zip
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resid-fp
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extfilt.cpp
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C/C++ Source or Header
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2009-01-03
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// ---------------------------------------------------------------------------
// This file is part of reSID, a MOS6581 SID emulator engine.
// Copyright (C) 2004 Dag Lem <resid@nimrod.no>
//
// This program 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.
//
// This program 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 this program; if not, write to the Free Software
// Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
// ---------------------------------------------------------------------------
#define __EXTFILT_CC__
#include "extfilt.h"
// ----------------------------------------------------------------------------
// Constructor.
// ----------------------------------------------------------------------------
ExternalFilterFP::ExternalFilterFP()
{
reset();
enable_filter(true);
set_chip_model(MOS6581FP);
set_clock_frequency(1e6f);
set_sampling_parameter(15915.6f);
}
// ----------------------------------------------------------------------------
// Enable filter.
// ----------------------------------------------------------------------------
void ExternalFilterFP::enable_filter(bool enable)
{
enabled = enable;
}
// ----------------------------------------------------------------------------
// Setup of the external filter sampling parameters.
// ----------------------------------------------------------------------------
void ExternalFilterFP::set_clock_frequency(float clock)
{
clock_frequency = clock;
_set_sampling_parameter();
}
void ExternalFilterFP::set_sampling_parameter(float freq)
{
pass_frequency = freq;
_set_sampling_parameter();
}
void ExternalFilterFP::_set_sampling_parameter()
{
// Low-pass: R = 10kOhm, C = 1000pF; w0l = 1/RC = 1/(1e4*1e-9) = 100000
// High-pass: R = 1kOhm, C = 10uF; w0h = 1/RC = 1/(1e3*1e-5) = 100
w0hp = 100.f / clock_frequency;
w0lp = pass_frequency * 2.f * M_PI_f / clock_frequency;
}
// ----------------------------------------------------------------------------
// Set chip model.
// ----------------------------------------------------------------------------
void ExternalFilterFP::set_chip_model(chip_model model)
{
if (model == MOS6581FP) {
// Approximate the DC output level to be removed if the external
// filter is turned off. (0x800 - wave_zero + voice DC) * maxenv * voices
// - extin offset...
mixer_DC = (-0x600 + 0x800) * 0xff * 3 - 0x20000;
}
else {
// No DC offsets in the MOS8580.
mixer_DC = 0;
}
}
// ----------------------------------------------------------------------------
// SID reset.
// ----------------------------------------------------------------------------
void ExternalFilterFP::reset()
{
// State of filter.
Vlp = 0;
Vhp = 0;
Vo = 0;
}