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aica: better sounding LPF 

Use 4 bits of exponent instead of 5 for the cut off frequency
Force sample to 0 if cut off freq is 0
Improve BIOS menu sounds
Issue #108
This commit is contained in:
Flyinghead 2023-11-02 18:33:14 +01:00
parent 5cfd3f0ba3
commit bafe07de85
1 changed files with 19 additions and 22 deletions
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41
core/hw/aica/sgc_if.cpp
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@ -74,19 +74,7 @@ static const double AEG_DSR_Time[64] =
920.0,790.0,690.0,550.0,460.0,390.0,340.0,270.0,230.0,200.0,170.0,140.0,110.0,98.0,85.0,68.0,57.0,49.0,43.0,34.0,
28.0,25.0,22.0,18.0,14.0,12.0,11.0,8.5,7.1,6.1,5.4,4.3,3.6,3.1
};
// These times come from the documentation but don't sound correct.
// HT uses the AEG decay times instead and it sounds better.
//static const double FEG_Time[] =
//{
// -1, -1, 472800.0, 405200.0, 354400.0, 283600.0, 236400.0, 202800.0,
// 177200.0, 142000.0, 118400.0, 101200.0, 88800.0, 70800.0, 59200.0, 50800.0,
// 44400.0, 35600.0, 29600.0, 25200.0, 22000.0, 17600.0, 14800.0, 12800.0,
// 11200.0, 8800.0, 7200.0, 6400.0, 5600.0, 4400.0, 3680.0, 3160.0,
// 2760.0, 2220.0, 1840.0, 1560.0, 1360.0, 1080.0, 920.0, 800.0,
// 680.0, 560.0, 440.0, 392.0, 340.0, 272.0, 228.0, 196.0,
// 172.0, 158.0, 136.0, 100.0, 88.0, 72.0, 56.0, 48.0,
// 44.0, 34.0, 28.0, 24.0, 22.0, 17.0, 14.0, 12.0
//};
static const float PLFOS_Scale[8] = { 0.f, 3.61f, 7.22f, 14.44f, 28.88f, 57.75f, 115.5f, 231.f };
static int PLFO_Scales[8][256];
@ -488,11 +476,16 @@ struct ChannelEx
if (FEG.active)
{
u32 fv = FEG.GetValue();
s32 f = (((fv & 0xFF) | 0x100) << 4) >> ((fv >> 8) ^ 0x1F);
f = std::max(1, f);
sample = f * sample + (0x2000 - f + FEG.q) * FEG.prev1 - FEG.q * FEG.prev2;
sample >>= 13;
sample = std::clamp(sample, -32768, 32767);
s32 f = (((fv & 0x1FF) | 0x200) << 3) >> ((fv >> 9) ^ 0xF);
if (f == 0) {
sample = 0;
}
else
{
sample = f * sample + (0x2000 - f + FEG.q) * FEG.prev1 - FEG.q * FEG.prev2;
sample >>= 13;
sample = std::clamp(sample, -32768, 32767);
}
FEG.prev2 = FEG.prev1;
FEG.prev1 = sample;
}
@ -822,6 +815,7 @@ struct ChannelEx
case 0x19://FNS,OCT
UpdatePitch();
UpdateAEG();
UpdateFEG();
break;
case 0x1C://ALFOS,ALFOWS,PLFOS
@ -1293,12 +1287,15 @@ void init()
for (int i=256;i<1024;i++)
tl_lut[i]=0;
for (int i=0;i<64;i++)
for (int i = 0; i < 64; i++)
{
AEG_ATT_SPS[i] = CalcAttackEgSteps(AEG_Attack_Time[i]);
AEG_DSR_SPS[i]=CalcEgSteps(AEG_DSR_Time[i]);
FEG_SPS[i] = CalcEgSteps(AEG_DSR_Time[i]);
//FEG_SPS[i] = CalcEgSteps(FEG_Time[i]);
AEG_DSR_SPS[i] = CalcEgSteps(AEG_DSR_Time[i]);
// The AEG range is 1024, while the FEG range is 8912.
// So decay times are x8 greater for FEG than AEG
// instead of x4 as mentioned in the doc.
// However it sounds better this way.
FEG_SPS[i] = AEG_DSR_SPS[i];
}
for (std::size_t i = 0; i < std::size(Chans); i++)
Chans[i].Init(i,aica_reg);