ref: b2f339168bf5b666f96067daf4de4c9f07f51c92
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 <string.h>
#include "st_i.h"
static st_effect_t st_band_effect;
/* 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
*/
static int st_band_getopts(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))
{
st_fail(st_band_effect.usage);
return (ST_EOF);
}
band->width = band->center / 2;
if ((n >= 2) && !sscanf(argv[1], "%f", &band->width))
{
st_fail(st_band_effect.usage);
return (ST_EOF);
}
return (ST_SUCCESS);
}
/*
* Prepare processing.
*/
static int st_band_start(eff_t effp)
{
band_t band = (band_t) effp->priv;
if (band->center > effp->ininfo.rate/2)
{
st_fail("Band: center must be < minimum data rate/2");
return (ST_EOF);
}
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;
if (effp->globalinfo->octave_plot_effect)
{
printf(
"title('SoX effect: %s centre=%g width=%g (rate=%u)')\n"
"xlabel('Frequency (Hz)')\n"
"ylabel('Amplitude Response (dB)')\n"
"Fs=%u;minF=10;maxF=Fs/2;\n"
"axis([minF maxF -75 25])\n"
"sweepF=logspace(log10(minF),log10(maxF),200);\n"
"grid on\n"
"[h,w]=freqz([%f 0 0],[1 %f %f],sweepF,Fs);\n"
"semilogx(w,20*log10(h),'b')\n"
"pause\n"
, effp->name, band->center, band->width
, effp->ininfo.rate, effp->ininfo.rate
, band->A
, band->B
, band->C
);
return ST_EOF;
}
return (ST_SUCCESS);
}
/*
* Processed signed long samples from ibuf to obuf.
* Return number of samples processed.
*/
static int st_band_flow(eff_t effp, const st_sample_t *ibuf, st_sample_t *obuf,
st_size_t *isamp, st_size_t *osamp)
{
band_t band = (band_t) effp->priv;
int len, done;
double d;
st_sample_t 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;
return(ST_SUCCESS);
}
/*
* Do anything required when you stop reading samples.
* Don't close input file!
*/
static int st_band_stop(eff_t effp UNUSED)
{
return (ST_SUCCESS); /* nothing to do */
}
static st_effect_t st_band_effect = {
"band",
"Usage: band [ -n ] center [ width ]",
0,
st_band_getopts,
st_band_start,
st_band_flow,
st_effect_nothing_drain,
st_band_stop,
st_effect_nothing
};
const st_effect_t *st_band_effect_fn(void)
{
return &st_band_effect;
}