Category : C Source Code
Archive   : SOX.ZIP
Filename : BAND.C

 
Output of file : BAND.C contained in archive : SOX.ZIP

/*
* July 5, 1991
* Copyright 1991 Lance Norskog And Sundry Contributors
* This source code is freely redistributable and may be used for
* any purpose. This copyright notice must be maintained.
* Lance Norskog And Sundry Contributors are not responsible for
* the consequences of using this software.
*/

/*
* Sound Tools Bandpass effect file.
*
* Algorithm: 2nd order recursive filter.
* Formula stolen from MUSIC56K, a toolkit of 56000 assembler stuff.
* Quote:
* This is a 2nd order recursive band pass filter of the form.
* y(n)= a * x(n) - b * y(n-1) - c * y(n-2)
* where :
* x(n) = "IN"
* "OUT" = y(n)
* c = EXP(-2*pi*cBW/S_RATE)
* b = -4*c/(1+c)*COS(2*pi*cCF/S_RATE)
* if cSCL=2 (i.e. noise input)
* a = SQT(((1+c)*(1+c)-b*b)*(1-c)/(1+c))
* else
* a = SQT(1-b*b/(4*c))*(1-c)
* endif
* note : cCF is the center frequency in Hertz
* cBW is the band width in Hertz
* cSCL is a scale factor, use 1 for pitched sounds
* use 2 for noise.
*/

#include
#include "st.h"

/* Private data for Bandpass effect */
typedef struct bandstuff {
float center;
float width;
double A, B, C;
double out1, out2;
short noise;
/* 50 bytes of data, 52 bytes long for allocation purposes. */
} *band_t;

/*
* Process options
*/
band_getopts(effp, n, argv)
eff_t effp;
int n;
char **argv;
{
band_t band = (band_t) effp->priv;

band->noise = 0;
if (n > 0 && !strcmp(argv[0], "-n")) {
band->noise = 1;
n--;
argv++;
}
if ((n < 1) || !sscanf(argv[0], "%f", &band->center))
fail("Usage: band [ -n ] center [ width ]");
band->width = band->center / 2;
if ((n >= 2) && !sscanf(argv[1], "%f", &band->width))
fail("Usage: band [ -n ] center [ width ]");
}

/*
* Prepare processing.
*/
band_start(effp)
eff_t effp;
{
band_t band = (band_t) effp->priv;
if (band->center > effp->ininfo.rate/2)
fail("Band: center must be < minimum data rate/2\n");

band->C = exp(-2*M_PI*band->width/effp->ininfo.rate);
band->B = -4*band->C/(1+band->C)*
cos(2*M_PI*band->center/effp->ininfo.rate);
if (band->noise)
band->A = sqrt(((1+band->C)*(1+band->C)-band->B *
band->B)*(1-band->C)/(1+band->C));
else
band->A = sqrt(1-band->B*band->B/(4*band->C))*(1-band->C);
band->out1 = band->out2 = 0.0;
}

/*
* Processed signed long samples from ibuf to obuf.
* Return number of samples processed.
*/

band_flow(effp, ibuf, obuf, isamp, osamp)
eff_t effp;
long *ibuf, *obuf;
int *isamp, *osamp;
{
band_t band = (band_t) effp->priv;
register counter, tablen;
int len, done;
register long mult;
register short *sinetab;
double d;
long l;

len = ((*isamp > *osamp) ? *osamp : *isamp);

/* yeah yeah yeah registers & integer arithmetic yeah yeah yeah */
for(done = 0; done < len; done++) {
l = *ibuf++;
d = (band->A * l - band->B * band->out1) - band->C * band->out2;
band->out2 = band->out1;
band->out1 = d;
*obuf++ = d;
}
}

/*
* Do anything required when you stop reading samples.
* Don't close input file!
*/
band_stop(effp)
eff_t effp;
{
/* nothing to do */
}



  3 Responses to “Category : C Source Code
Archive   : SOX.ZIP
Filename : BAND.C

  1. Very nice! Thank you for this wonderful archive. I wonder why I found it only now. Long live the BBS file archives!

  2. This is so awesome! 😀 I’d be cool if you could download an entire archive of this at once, though.

  3. But one thing that puzzles me is the “mtswslnkmcjklsdlsbdmMICROSOFT” string. There is an article about it here. It is definitely worth a read: http://www.os2museum.com/wp/mtswslnk/