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/*
* Snd_flt.cpp
* -----------
* Purpose: Calculation of resonant filter coefficients.
* Notes : Extended filter range was introduced in MPT 1.12 and went up to 8652 Hz.
* MPT 1.16 upped this to the current 10670 Hz.
* We have no way of telling whether a file was made with MPT 1.12 or 1.16 though.
* Authors: Olivier Lapicque
* OpenMPT Devs
* The OpenMPT source code is released under the BSD license. Read LICENSE for more details.
*/
#include "stdafx.h"
#include "Sndfile.h"
#include "Tables.h"
#include "../common/misc_util.h"
#include "mpt/base/numbers.hpp"
OPENMPT_NAMESPACE_BEGIN
// AWE32: cutoff = reg[0-255] * 31.25 + 100 -> [100Hz-8060Hz]
// EMU10K1 docs: cutoff = reg[0-127]*62+100
uint8 CSoundFile::FrequencyToCutOff(double frequency) const
{
// IT Cutoff is computed as cutoff = 110 * 2 ^ (0.25 + x/y), where x is the cutoff and y defines the filter range.
// Reversed, this gives us x = (log2(cutoff / 110) - 0.25) * y.
// <==========> Rewrite as x = (log2(cutoff) - log2(110) - 0.25) * y.
// <==========> Rewrite as x = (ln(cutoff) - ln(110) - 0.25*ln(2)) * y/ln(2).
// <4.8737671609324025>
double cutoff = (std::log(frequency) - 4.8737671609324025) * (m_SongFlags[SONG_EXFILTERRANGE] ? (20.0 / mpt::numbers::ln2) : (24.0 / mpt::numbers::ln2));
Limit(cutoff, 0.0, 127.0);
return mpt::saturate_round<uint8>(cutoff);
}
uint32 CSoundFile::CutOffToFrequency(uint32 nCutOff, int envModifier) const
{
MPT_ASSERT(nCutOff < 128);
float computedCutoff = static_cast<float>(nCutOff * (envModifier + 256)); // 0...127*512
float Fc;
if(GetType() != MOD_TYPE_IMF)
{
Fc = 110.0f * std::pow(2.0f, 0.25f + computedCutoff / (m_SongFlags[SONG_EXFILTERRANGE] ? 20.0f * 512.0f : 24.0f * 512.0f));
} else
{
// EMU8000: Documentation says the cutoff is in quarter semitones, with 0x00 being 125 Hz and 0xFF being 8 kHz
// The first half of the sentence contradicts the second, though.
Fc = 125.0f * std::pow(2.0f, computedCutoff * 6.0f / (127.0f * 512.0f));
}
int freq = mpt::saturate_round<int>(Fc);
Limit(freq, 120, 20000);
if(freq * 2 > (int)m_MixerSettings.gdwMixingFreq) freq = m_MixerSettings.gdwMixingFreq / 2;
return static_cast<uint32>(freq);
}
// Simple 2-poles resonant filter. Returns computed cutoff in range [0, 254] or -1 if filter is not applied.
int CSoundFile::SetupChannelFilter(ModChannel &chn, bool bReset, int envModifier) const
{
int cutoff = static_cast<int>(chn.nCutOff) + chn.nCutSwing;
int resonance = static_cast<int>(chn.nResonance & 0x7F) + chn.nResSwing;
Limit(cutoff, 0, 127);
Limit(resonance, 0, 127);
if(!m_playBehaviour[kMPTOldSwingBehaviour])
{
chn.nCutOff = (uint8)cutoff;
chn.nCutSwing = 0;
chn.nResonance = (uint8)resonance;
chn.nResSwing = 0;
}
// envModifier is in [-256, 256], so cutoff is in [0, 127 * 2] after this calculation.
const int computedCutoff = cutoff * (envModifier + 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(chn.rowCommand.IsNote() && !chn.rowCommand.IsPortamento() && !chn.nMasterChn && chn.triggerNote)
{
// 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-reset-envelope.it, filter-nna.it, FilterResetPatDelay.it
chn.dwFlags.reset(CHN_FILTER);
}
return -1;
}
chn.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, envModifier) * (2.0f * mpt::numbers::pi_v<float>);
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 MPT_FILTER_CONVERT(x) mpt::saturate_round<mixsample_t>((x) * (1 << MIXING_FILTER_PRECISION))
#else
#define MPT_FILTER_CONVERT(x) (x)
#endif
switch(chn.nFilterMode)
{
case FilterMode::HighPass:
chn.nFilter_A0 = MPT_FILTER_CONVERT(1.0f - fg);
chn.nFilter_B0 = MPT_FILTER_CONVERT(fb0);
chn.nFilter_B1 = MPT_FILTER_CONVERT(fb1);
#ifdef MPT_INTMIXER
chn.nFilter_HP = -1;
#else
chn.nFilter_HP = 1.0f;
#endif // MPT_INTMIXER
break;
default:
chn.nFilter_A0 = MPT_FILTER_CONVERT(fg);
chn.nFilter_B0 = MPT_FILTER_CONVERT(fb0);
chn.nFilter_B1 = MPT_FILTER_CONVERT(fb1);
#ifdef MPT_INTMIXER
if(chn.nFilter_A0 == 0)
chn.nFilter_A0 = 1; // Prevent silence at low filter cutoff and very high sampling rate
chn.nFilter_HP = 0;
#else
chn.nFilter_HP = 0;
#endif // MPT_INTMIXER
break;
}
#undef MPT_FILTER_CONVERT
if (bReset)
{
chn.nFilter_Y[0][0] = chn.nFilter_Y[0][1] = 0;
chn.nFilter_Y[1][0] = chn.nFilter_Y[1][1] = 0;
}
return computedCutoff;
}
OPENMPT_NAMESPACE_END
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