// Simple 2-poles resonant filter
void CSoundFile::SetupChannelFilter(ModChannel *pChn, bool bReset, int flt_modifier) const
{
int cutoff = (int)pChn->nCutOff + (int)pChn->nCutSwing;
int resonance = (int)(pChn->nResonance & 0x7F) + (int)pChn->nResSwing;
Limit(cutoff, 0, 127);
Limit(resonance, 0, 127);
if(!m_playBehaviour[kMPTOldSwingBehaviour])
{
pChn->nCutOff = (uint8)cutoff;
pChn->nCutSwing = 0;
pChn->nResonance = (uint8)resonance;
pChn->nResSwing = 0;
}
// flt_modifier is in [-256, 256], so cutoff is in [0, 127 * 2] after this calculation.
const int computedCutoff = cutoff * (flt_modifier + 256) / 256;
// Filtering is only ever done in IT if either cutoff is not full or if resonance is set.
if(m_playBehaviour[kITFilterBehaviour] && resonance == 0 && computedCutoff >= 254)
{
if(pChn->rowCommand.IsNote() && !pChn->rowCommand.IsPortamento() && !pChn->nMasterChn && m_SongFlags[SONG_FIRSTTICK])
{
// Z7F next to a note disables the filter, however in other cases this should not happen.
// Test cases: filter-reset.it, filter-reset-carry.it, filter-nna.it
pChn->dwFlags.reset(CHN_FILTER);
}
return;
}
pChn->dwFlags.set(CHN_FILTER);
// 2 * damping factor
const float dmpfac = std::pow(10.0f, -resonance * ((24.0f / 128.0f) / 20.0f));
const float fc = CutOffToFrequency(cutoff, flt_modifier) * (2.0f * (float)M_PI);
float d, e;
if(m_playBehaviour[kITFilterBehaviour] && !m_SongFlags[SONG_EXFILTERRANGE])
{
const float r = m_MixerSettings.gdwMixingFreq / fc;
d = dmpfac * r + dmpfac - 1.0f;
e = r * r;
} else
{
const float r = fc / m_MixerSettings.gdwMixingFreq;
d = (1.0f - 2.0f * dmpfac) * r;
LimitMax(d, 2.0f);
d = (2.0f * dmpfac - d) / r;
e = 1.0f / (r * r);
}
float fg = 1.0f / (1.0f + d + e);
float fb0 = (d + e + e) / (1 + d + e);
float fb1 = -e / (1.0f + d + e);
#if defined(MPT_INTMIXER)
#define FILTER_CONVERT(x) Util::Round<mixsample_t>((x) * (1 << MIXING_FILTER_PRECISION))
#else
#define FILTER_CONVERT(x) (x)
#endif
switch(pChn->nFilterMode)
{
case FLTMODE_HIGHPASS:
pChn->nFilter_A0 = FILTER_CONVERT(1.0f - fg);
pChn->nFilter_B0 = FILTER_CONVERT(fb0);
pChn->nFilter_B1 = FILTER_CONVERT(fb1);
#ifdef MPT_INTMIXER
pChn->nFilter_HP = -1;
#else
pChn->nFilter_HP = 1.0f;
#endif // MPT_INTMIXER
break;
default:
pChn->nFilter_A0 = FILTER_CONVERT(fg);
pChn->nFilter_B0 = FILTER_CONVERT(fb0);
pChn->nFilter_B1 = FILTER_CONVERT(fb1);
#ifdef MPT_INTMIXER
if(pChn->nFilter_A0 == 0)
pChn->nFilter_A0 = 1; // Prevent silence at low filter cutoff and very high sampling rate
pChn->nFilter_HP = 0;
#else
pChn->nFilter_HP = 0;
#endif // MPT_INTMIXER
break;
}
#undef FILTER_CONVERT
if (bReset)
{
pChn->nFilter_Y[0][0] = pChn->nFilter_Y[0][1] = 0;
pChn->nFilter_Y[1][0] = pChn->nFilter_Y[1][1] = 0;
}
}
// Simple 2-poles resonant filter
void CSoundFile::SetupChannelFilter(ModChannel *pChn, bool bReset, int flt_modifier) const
//----------------------------------------------------------------------------------------
{
int cutoff = (int)pChn->nCutOff + (int)pChn->nCutSwing;
int resonance = (int)(pChn->nResonance & 0x7F) + (int)pChn->nResSwing;
Limit(cutoff, 0, 127);
Limit(resonance, 0, 127);
if(!GetModFlag(MSF_OLDVOLSWING))
{
pChn->nCutOff = (uint8)cutoff;
pChn->nCutSwing = 0;
pChn->nResonance = (uint8)resonance;
pChn->nResSwing = 0;
}
float d, e;
// flt_modifier is in [-256, 256], so cutoff is in [0, 127 * 2] after this calculation.
const int computedCutoff = cutoff * (flt_modifier + 256) / 256;
// Filtering is only ever done in IT if either cutoff is not full or if resonance is set.
if(IsCompatibleMode(TRK_IMPULSETRACKER) && resonance == 0 && computedCutoff >= 254)
{
if(pChn->rowCommand.IsNote() && !pChn->rowCommand.IsPortamento() && !pChn->nMasterChn && m_SongFlags[SONG_FIRSTTICK])
{
// Z7F next to a note disables the filter, however in other cases this should not happen.
// Test cases: filter-reset.it, filter-reset-carry.it, filter-nna.it
pChn->dwFlags.reset(CHN_FILTER);
}
return;
}
pChn->dwFlags.set(CHN_FILTER);
if(UseITFilterMode())
{
const float freqParameterMultiplier = 128.0f / (24.0f * 256.0f);
// 2 ^ (i / 24 * 256)
float frequency = 110.0f * pow(2.0f, 0.25f + (float)computedCutoff * freqParameterMultiplier);
LimitMax(frequency, (float)(m_MixerSettings.gdwMixingFreq / 2));
const float r = (float)m_MixerSettings.gdwMixingFreq / (2.0f * (float)M_PI * frequency);
d = ITResonanceTable[resonance] * r + ITResonanceTable[resonance] - 1.0f;
e = r * r;
} else
{
float fc = (float)CutOffToFrequency(cutoff, flt_modifier);
const float dmpfac = pow(10.0f, -((24.0f / 128.0f) * (float)resonance) / 20.0f);
fc *= (float)(2.0f * (float)M_PI / (float)m_MixerSettings.gdwMixingFreq);
d = (1.0f - 2.0f * dmpfac) * fc;
LimitMax(d, 2.0f);
d = (2.0f * dmpfac - d) / fc;
e = pow(1.0f / fc, 2.0f);
}
float fg = 1.0f / (1.0f + d + e);
float fb0 = (d + e + e) / (1 + d + e);
float fb1 = -e / (1.0f + d + e);
#if defined(MPT_INTMIXER)
#define FILTER_CONVERT(x) static_cast<mixsample_t>((x) * (1 << MIXING_FILTER_PRECISION))
#else
#define FILTER_CONVERT(x) (x)
#endif
switch(pChn->nFilterMode)
{
case FLTMODE_HIGHPASS:
pChn->nFilter_A0 = FILTER_CONVERT(1.0f - fg);
pChn->nFilter_B0 = FILTER_CONVERT(fb0);
pChn->nFilter_B1 = FILTER_CONVERT(fb1);
#ifdef MPT_INTMIXER
pChn->nFilter_HP = -1;
#else
pChn->nFilter_HP = 1.0f;
#endif // MPT_INTMIXER
break;
default:
pChn->nFilter_A0 = FILTER_CONVERT(fg);
pChn->nFilter_B0 = FILTER_CONVERT(fb0);
pChn->nFilter_B1 = FILTER_CONVERT(fb1);
#ifdef MPT_INTMIXER
pChn->nFilter_HP = 0;
#else
pChn->nFilter_HP = 0;
#endif // MPT_INTMIXER
break;
}
#undef FILTER_CONVERT
if (bReset)
{
pChn->nFilter_Y[0][0] = pChn->nFilter_Y[0][1] = 0;
pChn->nFilter_Y[1][0] = pChn->nFilter_Y[1][1] = 0;
}
}
