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