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Src/Plugins/Input/in_mod/fir_proc.cpp
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172
Src/Plugins/Input/in_mod/fir_proc.cpp
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/*
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* This program is free software; you can redistribute it and modify it
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* under the terms of the GNU General Public License as published by the
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* Free Software Foundation; either version 2 of the license or (at your
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* option) any later version.
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*
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* Authors: Markus Fick <webmaster@mark-f.de> fir-resampler, technical information
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* Chris Moeller <chris@kode54.net> Table/struct file generator
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*
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*/
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#include <math.h>
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#include <stdio.h>
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/*
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------------------------------------------------------------------------------------------------
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fir interpolation doc,
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(derived from "an engineer's guide to fir digital filters", n.j. loy)
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calculate coefficients for ideal lowpass filter (with cutoff = fc in 0..1 (mapped to 0..nyquist))
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c[-N..N] = (i==0) ? fc : sin(fc*pi*i)/(pi*i)
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then apply selected window to coefficients
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c[-N..N] *= w(0..N)
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with n in 2*N and w(n) being a window function (see loy)
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then calculate gain and scale filter coefs to have unity gain.
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------------------------------------------------------------------------------------------------
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*/
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// quantizer scale of window coefs
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#define WFIR_QUANTBITS 14
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#define WFIR_QUANTSCALE (1L<<WFIR_QUANTBITS)
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#define WFIR_8SHIFT (WFIR_QUANTBITS-8)
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#define WFIR_16BITSHIFT (WFIR_QUANTBITS)
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// log2(number)-1 of precalculated taps range is [4..12]
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#define WFIR_FRACBITS 10
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#define WFIR_LUTLEN ((1L<<(WFIR_FRACBITS+1))+1)
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// number of samples in window
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#define WFIR_LOG2WIDTH 3
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#define WFIR_WIDTH (1L<<WFIR_LOG2WIDTH)
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#define WFIR_SMPSPERWING ((WFIR_WIDTH-1)>>1)
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// cutoff (1.0 == pi/2)
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#define WFIR_CUTOFF 0.90f
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#define WFIR_CUTOFFBITS 9
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#define WFIR_CUTOFFLEN ((1L<<(WFIR_CUTOFFBITS))+1)
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// wfir type
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#define WFIR_HANN 0
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#define WFIR_HAMMING 1
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#define WFIR_BLACKMANEXACT 2
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#define WFIR_BLACKMAN3T61 3
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#define WFIR_BLACKMAN3T67 4
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#define WFIR_BLACKMAN4T92 5
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#define WFIR_BLACKMAN4T74 6
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#define WFIR_KAISER4T 7
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#define WFIR_TYPE WFIR_BLACKMANEXACT
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// wfir help
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#ifndef M_zPI
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#define M_zPI 3.1415926535897932384626433832795
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#endif
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#define M_zEPS 1e-8
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#define M_zBESSELEPS 1e-21
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class CzWINDOWEDFIR
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{ public:
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CzWINDOWEDFIR( );
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~CzWINDOWEDFIR( );
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float coef( int _PCnr, float _POfs, float _PCut, int _PWidth, int _PType ) //float _PPos, float _PFc, int _PLen )
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{ double _LWidthM1 = _PWidth-1;
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double _LWidthM1Half = 0.5*_LWidthM1;
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double _LPosU = ((double)_PCnr - _POfs);
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double _LPos = _LPosU-_LWidthM1Half;
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double _LPIdl = 2.0*M_zPI/_LWidthM1;
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double _LWc,_LSi;
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if( fabs(_LPos)<M_zEPS )
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{ _LWc = 1.0;
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_LSi = _PCut;
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}
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else
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{ switch( _PType )
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{ case WFIR_HANN:
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_LWc = 0.50 - 0.50 * cos(_LPIdl*_LPosU);
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break;
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case WFIR_HAMMING:
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_LWc = 0.54 - 0.46 * cos(_LPIdl*_LPosU);
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break;
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case WFIR_BLACKMANEXACT:
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_LWc = 0.42 - 0.50 * cos(_LPIdl*_LPosU) + 0.08 * cos(2.0*_LPIdl*_LPosU);
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break;
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case WFIR_BLACKMAN3T61:
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_LWc = 0.44959 - 0.49364 * cos(_LPIdl*_LPosU) + 0.05677 * cos(2.0*_LPIdl*_LPosU);
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break;
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case WFIR_BLACKMAN3T67:
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_LWc = 0.42323 - 0.49755 * cos(_LPIdl*_LPosU) + 0.07922 * cos(2.0*_LPIdl*_LPosU);
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break;
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case WFIR_BLACKMAN4T92:
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_LWc = 0.35875 - 0.48829 * cos(_LPIdl*_LPosU) + 0.14128 * cos(2.0*_LPIdl*_LPosU) - 0.01168 * cos(3.0*_LPIdl*_LPosU);
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break;
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case WFIR_BLACKMAN4T74:
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_LWc = 0.40217 - 0.49703 * cos(_LPIdl*_LPosU) + 0.09392 * cos(2.0*_LPIdl*_LPosU) - 0.00183 * cos(3.0*_LPIdl*_LPosU);
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break;
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case WFIR_KAISER4T:
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_LWc = 0.40243 - 0.49804 * cos(_LPIdl*_LPosU) + 0.09831 * cos(2.0*_LPIdl*_LPosU) - 0.00122 * cos(3.0*_LPIdl*_LPosU);
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break;
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default:
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_LWc = 1.0;
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break;
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}
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_LPos *= M_zPI;
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_LSi = sin(_PCut*_LPos)/_LPos;
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}
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return (float)(_LWc*_LSi);
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}
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static signed short lut[WFIR_LUTLEN*WFIR_WIDTH];
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};
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signed short CzWINDOWEDFIR::lut[WFIR_LUTLEN*WFIR_WIDTH];
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CzWINDOWEDFIR::CzWINDOWEDFIR()
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{ int _LPcl;
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float _LPcllen = (float)(1L<<WFIR_FRACBITS); // number of precalculated lines for 0..1 (-1..0)
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float _LNorm = 1.0f / (float)(2.0f * _LPcllen);
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float _LCut = WFIR_CUTOFF;
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float _LScale = (float)WFIR_QUANTSCALE;
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float _LGain,_LCoefs[WFIR_WIDTH];
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for( _LPcl=0;_LPcl<WFIR_LUTLEN;_LPcl++ )
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{
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float _LOfs = ((float)_LPcl-_LPcllen)*_LNorm;
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int _LCc,_LIdx = _LPcl<<WFIR_LOG2WIDTH;
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for( _LCc=0,_LGain=0.0f;_LCc<WFIR_WIDTH;_LCc++ )
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{ _LGain += (_LCoefs[_LCc] = coef( _LCc, _LOfs, _LCut, WFIR_WIDTH, WFIR_TYPE ));
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}
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_LGain = 1.0f/_LGain;
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for( _LCc=0;_LCc<WFIR_WIDTH;_LCc++ )
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{ float _LCoef = (float)floor( 0.5 + _LScale*_LCoefs[_LCc]*_LGain );
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lut[_LIdx+_LCc] = (signed short)( (_LCoef<-_LScale)?-_LScale:((_LCoef>_LScale)?_LScale:_LCoef) );
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}
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}
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}
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CzWINDOWEDFIR::~CzWINDOWEDFIR()
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{ // nothing todo
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}
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CzWINDOWEDFIR sfir;
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// extern "C" signed short *fir_lut = &CzWINDOWEDFIR::lut[0];
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#define lut(a) CzWINDOWEDFIR::lut[a]
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int main()
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{
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FILE *f;
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int i;
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f = fopen("fir_table.h","w");
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fprintf(f,"static __int64 fir_lut[%d] = {\n",WFIR_LUTLEN * 2);
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for (i=0;i<(WFIR_LUTLEN*WFIR_WIDTH);i+=WFIR_WIDTH)
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{
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fprintf(f,"\t0x%.4hx%.4hx%.4hx%.4hx, 0x%.4hx%.4hx%.4hx%.4hx%s",
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lut(i+3), lut(i+2), lut(i+1), lut(i),
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lut(i+7), lut(i+6), lut(i+5), lut(i+4),
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(i<((WFIR_LUTLEN-1)*WFIR_WIDTH)) ? ",\n" : "\n};\n");
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}
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fclose(f);
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return(0);
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}
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