You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
325 lines
9.2 KiB
325 lines
9.2 KiB
// ---------------------------------------------------------------------------
|
|
// 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 __FILTER_CC__
|
|
#include "filter.h"
|
|
|
|
RESID_NAMESPACE_START
|
|
|
|
// Maximum cutoff frequency is specified as
|
|
// FCmax = 2.6e-5/C = 2.6e-5/2200e-12 = 11818.
|
|
//
|
|
// Measurements indicate a cutoff frequency range of approximately
|
|
// 220Hz - 18kHz on a MOS6581 fitted with 470pF capacitors. The function
|
|
// mapping FC to cutoff frequency has the shape of the tanh function, with
|
|
// a discontinuity at FCHI = 0x80.
|
|
// In contrast, the MOS8580 almost perfectly corresponds with the
|
|
// specification of a linear mapping from 30Hz to 12kHz.
|
|
//
|
|
// The mappings have been measured by feeding the SID with an external
|
|
// signal since the chip itself is incapable of generating waveforms of
|
|
// higher fundamental frequency than 4kHz. It is best to use the bandpass
|
|
// output at full resonance to pick out the cutoff frequency at any given
|
|
// FC setting.
|
|
//
|
|
// The mapping function is specified with spline interpolation points and
|
|
// the function values are retrieved via table lookup.
|
|
//
|
|
// NB! Cutoff frequency characteristics may vary, we have modeled two
|
|
// particular Commodore 64s.
|
|
/*
|
|
const fc_point Filter::f0_points_6581[] =
|
|
{
|
|
// FC f FCHI FCLO
|
|
// ----------------------------
|
|
{ 0, 220 }, // 0x00 - repeated end point
|
|
{ 0, 220 }, // 0x00
|
|
{ 128, 230 }, // 0x10
|
|
{ 256, 250 }, // 0x20
|
|
{ 384, 300 }, // 0x30
|
|
{ 512, 420 }, // 0x40
|
|
{ 640, 780 }, // 0x50
|
|
{ 768, 1600 }, // 0x60
|
|
{ 832, 2300 }, // 0x68
|
|
{ 896, 3200 }, // 0x70
|
|
{ 960, 4300 }, // 0x78
|
|
{ 992, 5000 }, // 0x7c
|
|
{ 1008, 5400 }, // 0x7e
|
|
{ 1016, 5700 }, // 0x7f
|
|
{ 1023, 6000 }, // 0x7f 0x07
|
|
{ 1023, 6000 }, // 0x7f 0x07 - discontinuity
|
|
{ 1024, 4600 }, // 0x80 -
|
|
{ 1024, 4600 }, // 0x80
|
|
{ 1032, 4800 }, // 0x81
|
|
{ 1056, 5300 }, // 0x84
|
|
{ 1088, 6000 }, // 0x88
|
|
{ 1120, 6600 }, // 0x8c
|
|
{ 1152, 7200 }, // 0x90
|
|
{ 1280, 9500 }, // 0xa0
|
|
{ 1408, 12000 }, // 0xb0
|
|
{ 1536, 14500 }, // 0xc0
|
|
{ 1664, 16000 }, // 0xd0
|
|
{ 1792, 17100 }, // 0xe0
|
|
{ 1920, 17700 }, // 0xf0
|
|
{ 2047, 18000 }, // 0xff 0x07
|
|
{ 2047, 18000 } // 0xff 0x07 - repeated end point
|
|
};
|
|
*/
|
|
/*
|
|
const fc_point Filter::f0_points_8580[] =
|
|
{
|
|
// FC f FCHI FCLO
|
|
// ----------------------------
|
|
{ 0, 0 }, // 0x00 - repeated end point
|
|
{ 0, 0 }, // 0x00
|
|
{ 128, 800 }, // 0x10
|
|
{ 256, 1600 }, // 0x20
|
|
{ 384, 2500 }, // 0x30
|
|
{ 512, 3300 }, // 0x40
|
|
{ 640, 4100 }, // 0x50
|
|
{ 768, 4800 }, // 0x60
|
|
{ 896, 5600 }, // 0x70
|
|
{ 1024, 6500 }, // 0x80
|
|
{ 1152, 7500 }, // 0x90
|
|
{ 1280, 8400 }, // 0xa0
|
|
{ 1408, 9200 }, // 0xb0
|
|
{ 1536, 9800 }, // 0xc0
|
|
{ 1664, 10500 }, // 0xd0
|
|
{ 1792, 11000 }, // 0xe0
|
|
{ 1920, 11700 }, // 0xf0
|
|
{ 2047, 12500 }, // 0xff 0x07
|
|
{ 2047, 12500 } // 0xff 0x07 - repeated end point
|
|
};
|
|
*/
|
|
|
|
// ----------------------------------------------------------------------------
|
|
// Constructor.
|
|
// ----------------------------------------------------------------------------
|
|
Filter::Filter()
|
|
{
|
|
fc = 0;
|
|
|
|
res = 0;
|
|
|
|
filt = 0;
|
|
|
|
voice3off = 0;
|
|
|
|
hp_bp_lp = 0;
|
|
|
|
vol = 0;
|
|
|
|
// State of filter.
|
|
Vhp = 0;
|
|
Vbp = 0;
|
|
Vlp = 0;
|
|
Vnf = 0;
|
|
|
|
enable_filter(true);
|
|
/*
|
|
// Create mappings from FC to cutoff frequency.
|
|
interpolate(f0_points_6581, f0_points_6581
|
|
+ sizeof(f0_points_6581)/sizeof(*f0_points_6581) - 1,
|
|
PointPlotter<sound_sample>(f0_6581), 1.0);
|
|
|
|
interpolate(f0_points_8580, f0_points_8580
|
|
+ sizeof(f0_points_8580)/sizeof(*f0_points_8580) - 1,
|
|
PointPlotter<sound_sample>(f0_8580), 1.0);
|
|
*/
|
|
// set_chip_model(MOS6581);
|
|
{//instead:
|
|
mixer_DC = -0xfff*0xff/18 >> 7;
|
|
|
|
//f0 = f0_6581;
|
|
// f0_points = f0_points_6581;
|
|
// f0_count = sizeof(f0_points_6581)/sizeof(*f0_points_6581);
|
|
set_w0();
|
|
set_Q();
|
|
}
|
|
|
|
}
|
|
|
|
|
|
// ----------------------------------------------------------------------------
|
|
// Enable filter.
|
|
// ----------------------------------------------------------------------------
|
|
void Filter::enable_filter(bool enable)
|
|
{
|
|
enabled = enable;
|
|
}
|
|
|
|
|
|
// ----------------------------------------------------------------------------
|
|
// Set chip model.
|
|
// ----------------------------------------------------------------------------
|
|
/*
|
|
void Filter::set_chip_model(chip_model model)
|
|
{
|
|
if (model == MOS6581) {
|
|
// The mixer has a small input DC offset. This is found as follows:
|
|
//
|
|
// The "zero" output level of the mixer measured on the SID audio
|
|
// output pin is 5.50V at zero volume, and 5.44 at full
|
|
// volume. This yields a DC offset of (5.44V - 5.50V) = -0.06V.
|
|
//
|
|
// The DC offset is thus -0.06V/1.05V ~ -1/18 of the dynamic range
|
|
// of one voice. See voice.cc for measurement of the dynamic
|
|
// range.
|
|
|
|
mixer_DC = -0xfff*0xff/18 >> 7;
|
|
|
|
f0 = f0_6581;
|
|
f0_points = f0_points_6581;
|
|
f0_count = sizeof(f0_points_6581)/sizeof(*f0_points_6581);
|
|
}
|
|
else {
|
|
// No DC offsets in the MOS8580.
|
|
mixer_DC = 0;
|
|
|
|
f0 = f0_8580;
|
|
f0_points = f0_points_8580;
|
|
f0_count = sizeof(f0_points_8580)/sizeof(*f0_points_8580);
|
|
}
|
|
|
|
set_w0();
|
|
set_Q();
|
|
}
|
|
*/
|
|
|
|
|
|
// ----------------------------------------------------------------------------
|
|
// SID reset.
|
|
// ----------------------------------------------------------------------------
|
|
void Filter::reset()
|
|
{
|
|
fc = 0;
|
|
|
|
res = 0;
|
|
|
|
filt = 0;
|
|
|
|
voice3off = 0;
|
|
|
|
hp_bp_lp = 0;
|
|
|
|
vol = 0;
|
|
|
|
// State of filter.
|
|
Vhp = 0;
|
|
Vbp = 0;
|
|
Vlp = 0;
|
|
Vnf = 0;
|
|
|
|
set_w0();
|
|
set_Q();
|
|
}
|
|
|
|
|
|
// ----------------------------------------------------------------------------
|
|
// Register functions.
|
|
// ----------------------------------------------------------------------------
|
|
void Filter::writeFC_LO(reg8 fc_lo)
|
|
{
|
|
fc = (fc & 0x7f8) | (fc_lo & 0x007);
|
|
set_w0();
|
|
}
|
|
|
|
void Filter::writeFC_HI(reg8 fc_hi)
|
|
{
|
|
fc = (((unsigned int)fc_hi << 3) & 0x7f8) | (fc & 0x007);
|
|
set_w0();
|
|
}
|
|
|
|
void Filter::writeRES_FILT(reg8 res_filt)
|
|
{
|
|
res = (res_filt >> 4) & 0x0f;
|
|
set_Q();
|
|
|
|
filt = res_filt & 0x0f;
|
|
}
|
|
|
|
void Filter::writeMODE_VOL(reg8 mode_vol)
|
|
{
|
|
voice3off = mode_vol & 0x80;
|
|
|
|
hp_bp_lp = (mode_vol >> 4) & 0x07;
|
|
|
|
vol = mode_vol & 0x0f;
|
|
}
|
|
|
|
// Set filter cutoff frequency.
|
|
void Filter::set_w0()
|
|
{
|
|
const float pi = 3.1415926535897932385;
|
|
|
|
// Multiply with 1.048576 to facilitate division by 1 000 000 by right-
|
|
// shifting 20 times (2 ^ 20 = 1048576).
|
|
w0 = static_cast<sound_sample>(2.0*pi*f0[fc]*1.048576);
|
|
|
|
// Limit f0 to 16kHz to keep 1 cycle filter stable.
|
|
const sound_sample w0_max_1 = static_cast<sound_sample>(2.0*pi*16000.0*1.048576);
|
|
w0_ceil_1 = w0 <= w0_max_1 ? w0 : w0_max_1;
|
|
|
|
// Limit f0 to 4kHz to keep delta_t cycle filter stable.
|
|
const sound_sample w0_max_dt = static_cast<sound_sample>(2.0*pi*4000.0*1.048576);
|
|
w0_ceil_dt = w0 <= w0_max_dt ? w0 : w0_max_dt;
|
|
}
|
|
|
|
// Set filter resonance.
|
|
void Filter::set_Q()
|
|
{
|
|
// Q is controlled linearly by res. Q has approximate range [0.707, 1.7].
|
|
// As resonance is increased, the filter must be clocked more often to keep
|
|
// stable.
|
|
|
|
// The coefficient 1024 is dispensed of later by right-shifting 10 times
|
|
// (2 ^ 10 = 1024).
|
|
_1024_div_Q = static_cast<sound_sample>(1024.0/(0.707 + 1.0*res/15.0));
|
|
}
|
|
|
|
// ----------------------------------------------------------------------------
|
|
// Spline functions.
|
|
// ----------------------------------------------------------------------------
|
|
|
|
// ----------------------------------------------------------------------------
|
|
// Return the array of spline interpolation points used to map the FC register
|
|
// to filter cutoff frequency.
|
|
// ----------------------------------------------------------------------------
|
|
/*
|
|
void Filter::fc_default(const fc_point*& points, int& count)
|
|
{
|
|
points = f0_points;
|
|
count = f0_count;
|
|
}
|
|
*/
|
|
// ----------------------------------------------------------------------------
|
|
// Given an array of interpolation points p with n points, the following
|
|
// statement will specify a new FC mapping:
|
|
// interpolate(p, p + n - 1, filter.fc_plotter(), 1.0);
|
|
// Note that the x range of the interpolation points *must* be [0, 2047],
|
|
// and that additional end points *must* be present since the end points
|
|
// are not interpolated.
|
|
// ----------------------------------------------------------------------------
|
|
/*
|
|
PointPlotter<sound_sample> Filter::fc_plotter()
|
|
{
|
|
return PointPlotter<sound_sample>(f0);
|
|
}
|
|
*/
|
|
RESID_NAMESPACE_STOP
|
|
|