ref: 7b8a31bb5c241bd5db253ed28c2a8325711e8f7f
dir: /src/band.c/
/*
* 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.
*
*
* July 1, 1999 - Jan Paul Schmidt <jps@fundament.org>
*
* This looks like the resonator band pass in SPKit. It's a
* second order all-pole (IIR) band-pass filter described
* at the pages 186 - 189 in
* Dodge, Charles & Jerse, Thomas A. 1985:
* Computer Music -- Synthesis, Composition and Performance.
* New York: Schirmer Books.
* Reference from the SPKit manual.
*/
#include <math.h>
#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
*/
void 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.
*/
void 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.
*/
void band_flow(effp, ibuf, obuf, isamp, osamp)
eff_t effp;
LONG *ibuf, *obuf;
int *isamp, *osamp;
{
band_t band = (band_t) effp->priv;
int len, done;
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;
}
*isamp = len;
*osamp = len;
}
/*
* Do anything required when you stop reading samples.
* Don't close input file!
*/
void band_stop(effp)
eff_t effp;
{
/* nothing to do */
}