public void set_chip_model(SIDDefs.chip_model model)
{
if (model == SIDDefs.chip_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.java for measurement of the dynamic
// range.
mixer_DC = -0xfff * 0xff / 18 >> 7;
f0 = f0_6581;
f0_points = f0_points_6581;
f0_count = f0_points_6581.Length;
}
else
{
// No DC offsets in the MOS8580.
mixer_DC = 0;
f0 = f0_8580;
f0_points = f0_points_8580;
f0_count = f0_points_8580.Length;
}
set_w0();
set_Q();
}
public void set_chip_model(SIDDefs.chip_model model)
{
voice0.set_chip_model(model);
voice1.set_chip_model(model);
voice2.set_chip_model(model);
filter.set_chip_model(model);
extfilt.set_chip_model(model);
}
public void set_chip_model(SIDDefs.chip_model model)
{
if (model == SIDDefs.chip_model.MOS6581)
{
// Maximum mixer DC output level; to be removed if the external
// filter is turned off: ((wave DC + voice DC) * voices + mixer DC) * volume
// See Voice.cs and Filter.cs for an explanation of the values.
mixer_DC = ((((0x800 - 0x380) + 0x800) * 0xff * 3 - 0xfff * 0xff / 18) >> 7) * 0x0f;
}
else
{
// No DC offsets in the MOS8580.
mixer_DC = 0;
}
}
public void set_chip_model(SIDDefs.chip_model model)
{
if (model == SIDDefs.chip_model.MOS6581)
{
wave__ST = memWave6581.wave6581__ST;
wave_P_T = memWave6581.wave6581_P_T;
wave_PS_ = memWave6581.wave6581_PS_;
wave_PST = memWave6581.wave6581_PST;
}
else
{
wave__ST = memWave8580.wave8580__ST;
wave_P_T = memWave8580.wave8580_P_T;
wave_PS_ = memWave8580.wave8580_PS_;
wave_PST = memWave8580.wave8580_PST;
}
}
public void set_chip_model(SIDDefs.chip_model model)
{
wave.set_chip_model(model);
if (model == SIDDefs.chip_model.MOS6581)
{
// The waveform D/A converter introduces a DC offset in the signal
// to the envelope multiplying D/A converter. The "zero" level of
// the waveform D/A converter can be found as follows:
//
// Measure the "zero" voltage of voice 3 on the SID audio output
// pin, routing only voice 3 to the mixer ($d417 = $0b, $d418 =
// $0f, all other registers zeroed).
//
// Then set the sustain level for voice 3 to maximum and search for
// the waveform output value yielding the same voltage as found
// above. This is done by trying out different waveform output
// values until the correct value is found, e.g. with the following
// program:
//
// lda #$08
// sta $d412
// lda #$0b
// sta $d417
// lda #$0f
// sta $d418
// lda #$f0
// sta $d414
// lda #$21
// sta $d412
// lda #$01
// sta $d40e
//
// ldx #$00
// lda #$38 ; Tweak this to find the "zero" level
// l cmp $d41b
// bne l
// stx $d40e ; Stop frequency counter - freeze waveform output
// brk
//
// The waveform output range is 0x000 to 0xfff, so the "zero"
// level should ideally have been 0x800. In the measured chip, the
// waveform output "zero" level was found to be 0x380 (i.e. $d41b
// = 0x38) at 5.94V.
wave_zero = 0x380;
// The envelope multiplying D/A converter introduces another DC
// offset. This is isolated by the following measurements:
//
// * The "zero" output level of the mixer at full volume is 5.44V.
// * Routing one voice to the mixer at full volume yields
// 6.75V at maximum voice output (wave = 0xfff, sustain = 0xf)
// 5.94V at "zero" voice output (wave = any, sustain = 0x0)
// 5.70V at minimum voice output (wave = 0x000, sustain = 0xf)
// * The DC offset of one voice is (5.94V - 5.44V) = 0.50V
// * The dynamic range of one voice is |6.75V - 5.70V| = 1.05V
// * The DC offset is thus 0.50V/1.05V ~ 1/2 of the dynamic range.
//
// Note that by removing the DC offset, we get the following ranges
// for
// one voice:
// y > 0: (6.75V - 5.44V) - 0.50V = 0.81V
// y < 0: (5.70V - 5.44V) - 0.50V = -0.24V
// The scaling of the voice amplitude is not symmetric about y = 0;
// this follows from the DC level in the waveform output.
voice_DC = 0x800 * 0xff;
}
else
{
// No DC offsets in the MOS8580.
wave_zero = 0x800;
voice_DC = 0;
}
}
