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/* * This source code is public domain. * * Authors: Olivier Lapicque <olivierl@jps.net> */ #include "libmodplug.h" // AWE32: cutoff = reg[0-255] * 31.25 + 100 -> [100Hz-8060Hz] // EMU10K1 docs: cutoff = reg[0-127]*62+100 #define FILTER_PRECISION 8192 #ifndef NO_FILTER DWORD CSoundFile_CutOffToFrequency(CSoundFile *_this, UINT nCutOff, int flt_modifier) //----------------------------------------------------------------------- { float Fc; if (_this->m_dwSongFlags & SONG_EXFILTERRANGE) Fc = 110.0f * SDL_pow(2.0f, 0.25f + ((float)(nCutOff*(flt_modifier+256)))/(21.0f*512.0f)); else Fc = 110.0f * SDL_pow(2.0f, 0.25f + ((float)(nCutOff*(flt_modifier+256)))/(24.0f*512.0f)); LONG freq = (LONG)Fc; if (freq < 120) return 120; if (freq > 10000) return 10000; if (freq*2 > (LONG)_this->gdwMixingFreq) freq = _this->gdwMixingFreq>>1; return (DWORD)freq; } // Simple 2-poles resonant filter void CSoundFile_SetupChannelFilter(CSoundFile *_this, MODCHANNEL *pChn, BOOL bReset, int flt_modifier) //---------------------------------------------------------------------------------------- { float fc = (float)CSoundFile_CutOffToFrequency(_this, pChn->nCutOff, flt_modifier); float fs = (float)_this->gdwMixingFreq; float fg, fb0, fb1; fc *= (float)(2.0*3.14159265358/fs); float dmpfac = SDL_pow(10.0f, -((24.0f / 128.0f)*(float)pChn->nResonance) / 20.0f); float d = (1.0f-2.0f*dmpfac)* fc; if (d>2.0) d = 2.0; d = (2.0f*dmpfac - d)/fc; float e = SDL_pow(1.0f/fc,2.0f); fg=1/(1+d+e); fb0=(d+e+e)/(1+d+e); fb1=-e/(1+d+e); pChn->nFilter_A0 = (int)(fg * FILTER_PRECISION); pChn->nFilter_B0 = (int)(fb0 * FILTER_PRECISION); pChn->nFilter_B1 = (int)(fb1 * FILTER_PRECISION); if (bReset) { pChn->nFilter_Y1 = pChn->nFilter_Y2 = 0; pChn->nFilter_Y3 = pChn->nFilter_Y4 = 0; } pChn->dwFlags |= CHN_FILTER; } #endif // NO_FILTER
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