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/*
* Schism Tracker - a cross-platform Impulse Tracker clone
* copyright (c) 2003-2005 Storlek <storlek@rigelseven.com>
* copyright (c) 2005-2008 Mrs. Brisby <mrs.brisby@nimh.org>
* copyright (c) 2009 Storlek & Mrs. Brisby
* copyright (c) 2010-2012 Storlek
* URL: http://schismtracker.org/
*
* 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
*/
#include "sndfile.h"
#include "cmixer.h"
#include <math.h>
// LUT for 2 * damping factor
static const float resonance_table[128] = {
1.0000000000000000f, 0.9786446094512940f, 0.9577452540397644f, 0.9372922182083130f,
0.9172759056091309f, 0.8976871371269226f, 0.8785166740417481f, 0.8597555756568909f,
0.8413951396942139f, 0.8234267830848694f, 0.8058421611785889f, 0.7886331081390381f,
0.7717915177345276f, 0.7553095817565918f, 0.7391796708106995f, 0.7233941555023193f,
0.7079457640647888f, 0.6928272843360901f, 0.6780316829681397f, 0.6635520458221436f,
0.6493816375732422f, 0.6355138421058655f, 0.6219421625137329f, 0.6086603403091431f,
0.5956621170043945f, 0.5829415321350098f, 0.5704925656318665f, 0.5583094954490662f,
0.5463865399360657f, 0.5347182154655457f, 0.5232990980148315f, 0.5121238231658936f,
0.5011872053146362f, 0.4904841780662537f, 0.4800096750259399f, 0.4697588682174683f,
0.4597269892692566f, 0.4499093294143677f, 0.4403013288974762f, 0.4308985173702240f,
0.4216965138912201f, 0.4126909971237183f, 0.4038778245449066f, 0.3952528536319733f,
0.3868120610713959f, 0.3785515129566193f, 0.3704673945903778f, 0.3625559210777283f,
0.3548133969306946f, 0.3472362160682678f, 0.3398208320140839f, 0.3325638175010681f,
0.3254617750644684f, 0.3185114264488220f, 0.3117094635963440f, 0.3050527870655060f,
0.2985382676124573f, 0.2921628654003143f, 0.2859236001968384f, 0.2798175811767578f,
0.2738419771194458f, 0.2679939568042755f, 0.2622708380222321f, 0.2566699385643005f,
0.2511886358261108f, 0.2458244115114212f, 0.2405747324228287f, 0.2354371547698975f,
0.2304092943668366f, 0.2254888117313385f, 0.2206734120845795f, 0.2159608304500580f,
0.2113489061594009f, 0.2068354636430740f, 0.2024184018373489f, 0.1980956792831421f,
0.1938652694225311f, 0.1897251904010773f, 0.1856735348701477f, 0.1817083954811096f,
0.1778279393911362f, 0.1740303486585617f, 0.1703138649463654f, 0.1666767448186874f,
0.1631172895431519f, 0.1596338599920273f, 0.1562248021364212f, 0.1528885662555695f,
0.1496235728263855f, 0.1464282870292664f, 0.1433012634515762f, 0.1402409970760346f,
0.1372461020946503f, 0.1343151479959488f, 0.1314467936754227f, 0.1286396980285645f,
0.1258925348520279f, 0.1232040524482727f, 0.1205729842185974f, 0.1179980933666229f,
0.1154781952500343f, 0.1130121126770973f, 0.1105986908078194f, 0.1082368120551109f,
0.1059253737330437f, 0.1036632955074310f, 0.1014495193958283f, 0.0992830246686935f,
0.0971627980470657f, 0.0950878411531448f, 0.0930572077631950f, 0.0910699293017387f,
0.0891250967979431f, 0.0872217938303947f, 0.0853591337800026f, 0.0835362523794174f,
0.0817523002624512f, 0.0800064504146576f, 0.0782978758215904f, 0.0766257941722870f,
0.0749894231557846f, 0.0733879879117012f, 0.0718207582831383f, 0.0702869966626167f,
0.0687859877943993f, 0.0673170387744904f, 0.0658794566988945f, 0.0644725710153580f,
};
// Simple 2-poles resonant filter
//
// XXX freq WAS unused but is now mix_frequency!
//
#define FREQ_PARAM_MULT (128.0 / (24.0 * 256.0))
void setup_channel_filter(song_voice_t *chan, int reset, int flt_modifier, int freq)
{
int cutoff = chan->cutoff;
int resonance = chan->resonance;
float frequency, r, d, e, fg, fb0, fb1;
cutoff = cutoff * (flt_modifier + 256) / 256;
if (cutoff > 255)
cutoff = 255;
if (resonance > 255)
resonance = 255;
// TODO: The enabling/disabling of channel filter is a bit more complex.
// More info in snd_flt.cpp in OpenMPT and filter-reset.it, filter-reset-carry.it
// and filter-nna.it from https://wiki.openmpt.org/Development:_Test_Cases/IT
// Should be 255, but Zxx cutoff is limited to 127, so...
if (cutoff < 254)
chan->flags |= CHN_FILTER;
else
cutoff = 255;
// 2 ^ (i / 24 * 256)
frequency = 110.0 * powf(2.0, (float) cutoff * FREQ_PARAM_MULT + 0.25);
if (frequency > freq / 2.0)
frequency = freq / 2.0;
r = freq / (2.0 * M_PI * frequency);
d = resonance_table[resonance] * r + resonance_table[resonance] - 1.0;
e = r * r;
fg = 1.0 / (1.0 + d + e);
fb0 = (d + e + e) / (1.0 + d + e);
fb1 = -e / (1.0 + d + e);
chan->filter_a0 = (int32_t)(fg * (1 << FILTERPRECISION));
chan->filter_b0 = (int32_t)(fb0 * (1 << FILTERPRECISION));
chan->filter_b1 = (int32_t)(fb1 * (1 << FILTERPRECISION));
if (reset) {
chan->filter_y1 = chan->filter_y2 = 0;
chan->filter_y3 = chan->filter_y4 = 0;
}
}
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