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#include <math.h>
#include <stdio.h>
/*
#include <carl/carl.h>
#include <carl/sndio.h>
#include <carl/defaults.h>
*/
/*-------------------------------------------------------
median.c
This program implements a median filter. The median filter
is a nonlinear filter; its output at each point in
time is the median of the N most recent input values.
The attraction of such a filter is that - unlike a linear
filter - it can remove glitches while still following
step changes perfectly. On the other hand, the median
filter does introduce a signal-dependent distortion
which depends also on the value of N.
cc -O median.c -lcarl -lm -o median
-------------------------------------------------------*/
main(argc, argv)
int argc; char **argv;
{
int i, /* pointer to current sample in buffer */
j,
N = 9, /* number of sample to mediate over */
N2; /* N / 2 */
float *buf, /* buffer for N most recent samples */
min, /* temporary minimum */
max, /* temporary maximum */
med = 0., /* median */
new, /* current input sample */
old, /* sample being replaced */
srate = 1.; /* sample rate */
char ch;
char *dbuf; /* buffer for strings read from header */
PROP *proplist; /* from header on stdin */
float dummy; /* pl, to throw away rmsamps */
/* Read header from stdin. */
if (isatty(0))
usage(1);
if ((proplist = getheader(stdin)) != NULL) { /* there is a header */
if ((dbuf = getprop(stdin,H_SRATE)) != NULL) {
srate = atof(dbuf); /* get input srate */
}
}
/* Call crack to interpret commandline. */
while ((ch = crack(argc, argv, "R|", 1)) != NULL){
switch (ch){
case 'R': srate = sfexpr(arg_option, 1.0); break;
}
}
arg_index = 0; /* reset for second call to crack() */
while ((ch = crack(argc, argv, "R|w|m|h", 0)) != NULL){
switch (ch){
case 'w': N = sfexpr(arg_option, srate); break;
case 'R': break;
case 'h': usage(0);
default: usage(1);
}
}
if (N%2 == 0)
N--;
N2 = (N-1) / 2;
printf("%d %d\n",N,N2);
/* Initialization. */
if ((buf = (float *) calloc(N,sizeof(float))) == NULL)
malerr("median: insufficient memory",1);
for (i = 0; i < N2; i++){
if (getfloat(&new) <= 0) new = 0;
getfloat(&dummy);
buf[i] = new;
buf[N-i-1] = new;
if (new > med){
min = 1e6;
for (j = 0; j <= i; j++)
if ((buf[j] >= med) && (buf[j] < min))
min = buf[j];
med = min;
}
if (new < med){
max = -1e6;
for (j = 0; j <= i; j++)
if ((buf[j] <= med) && (buf[j] > max))
max = buf[j];
med = max;
}
}
buf[N2] = med;
i = N2;
/* Main loop: buf contains the N most recent inputs. If input(n) > median
and input(n-N) > median, then median is unchanged. The same applies
if both are less than the median. Hence the median is only re-
calculated when input(n) > median and input(n-N) < median or (vice
versa). The new median is simply the next largest (or smallest) of
the N most recent inputs. */
while (getfloat(&new) > 0){
getfloat(&dummy);
old = buf[i];
buf[i] = new;
if (++i >= N) i = 0;
if ((new > med) && (old <= med)){
min = 1e6;
for (j = 0; j < N; j++)
if ((buf[j] >= med) && (buf[j] < min))
min = buf[j];
med = min;
}
if ((new < med) && (old >= med)){
max = -1e6;
for (j = 0; j < N; j++)
if ((buf[j] <= med) && (buf[j] > max))
max = buf[j];
med = max;
}
putfloat(&med);
putfloat(&dummy);
}
flushfloat();
}
usage(exitcode)
int exitcode;
{
fprintf(stderr, "%s%s%s%s",
"median [flag] < floatsams > output\n",
" flags:\n",
" -wN\t set window size to N seconds (default: 9S).\n",
" -RN\t set sample rate to N (default = read from stdin).\n"
);
exit(exitcode);
}
malerr(str, ex)
char *str;
int ex;
{
fprintf(stderr, "%s\n", str);
exit(ex);
}
These are the contents of the former NiCE NeXT User Group NeXTSTEP/OpenStep software archive, currently hosted by Netfuture.ch.