ref: 7cfe6fdb10ec6fe6cb9c7e80b28df0ed9abfd1e5
dir: /src/highp.c/
/*
* Sound Tools High-Pass effect file.
*
* (C) 2000 Chris Bagwell <cbagwell@sprynet.com>
* See License file for further copyright information.
*
* Algorithm: Recursive single pole high-pass filter
*
* Reference: The Scientist and Engineer's Guide to Digital Processing
*
* output[N] = A0 * input[N] + A1 * input[N-1] + B1 * output[N-1]
*
* X = exp(-2.0 * pi * Fc)
* A0 = (1 + X) / 2
* A1 = -(1 + X) / 2
* B1 = X
* Fc = cutoff freq / sample rate
*
* Mimics an RC high-pass filter:
*
* || C
* ----||--------->
* || |
* <
* > R
* <
* |
* V
*
*/
#include <math.h>
#include "st.h"
/* Private data for Highpass effect */
typedef struct highpstuff {
float cutoff;
double A0, A1, B1;
double inm1, outm1;
} *highp_t;
/*
* Process options
*/
int st_highp_getopts(effp, n, argv)
eff_t effp;
int n;
char **argv;
{
highp_t highp = (highp_t) effp->priv;
if ((n < 1) || !sscanf(argv[0], "%f", &highp->cutoff))
{
st_fail("Usage: highp cutoff");
return (ST_EOF);
}
return (ST_SUCCESS);
}
/*
* Prepare processing.
*/
int st_highp_start(effp)
eff_t effp;
{
highp_t highp = (highp_t) effp->priv;
if (highp->cutoff > effp->ininfo.rate/2)
{
st_fail("Highpass: cutoff must be < sample rate / 2 (Nyquest rate)\n");
return (ST_EOF);
}
highp->B1 = exp((-2.0 * M_PI * (highp->cutoff / effp->ininfo.rate)));
highp->A0 = (1 + highp->B1) / 2;
highp->A1 = (-1 * (1 + highp->B1)) / 2;
highp->inm1 = 0.0;
highp->outm1 = 0.0;
return (ST_SUCCESS);
}
/*
* Processed signed long samples from ibuf to obuf.
* Return number of samples processed.
*/
int st_highp_flow(effp, ibuf, obuf, isamp, osamp)
eff_t effp;
LONG *ibuf, *obuf;
LONG *isamp, *osamp;
{
highp_t highp = (highp_t) effp->priv;
int len, done;
double d;
LONG l;
len = ((*isamp > *osamp) ? *osamp : *isamp);
for(done = 0; done < len; done++) {
l = *ibuf++;
d = highp->A0 * l +
highp->A1 * highp->inm1 +
highp->B1 * highp->outm1;
if (d < -2147483647L)
d = -2147483647L;
else if (d > 2147483647L)
d = 2147483647L;
highp->inm1 = l;
highp->outm1 = d;
*obuf++ = d;
}
*isamp = len;
*osamp = len;
return (ST_SUCCESS);
}
/*
* Do anything required when you stop reading samples.
* Don't close input file!
*/
int st_highp_stop(effp)
eff_t effp;
{
/* nothing to do */
return (ST_SUCCESS);
}