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usrp/fft.c: added support for averaging of FFT results before dumping

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- fft.c (usage, main): added optional averaging parameter for -d (dump)
- fft.c (do_fft): split the sample into several parts, FFT each of them
  individually, and average the FFT results
This commit is contained in:
Werner Almesberger 2011-03-03 17:46:41 -03:00
parent 95a9e12e2e
commit c98b91656a
1 changed files with 44 additions and 19 deletions
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63
usrp/fft.c
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@ -91,13 +91,14 @@ static void fft_real(int n, const float *re, const float *im, double *res)
}
static void do_fft(int skip, int dump, int low, int high, double threshold)
static void do_fft(int skip, int dump, int low, int high, double threshold,
int split)
{
float c[2];
float *re = NULL, *im = NULL;
double *res;
double *out, *res;
int e = 0, n = 0;
int i;
int i, j, off;
double a;
while (1) {
@ -138,28 +139,46 @@ static void do_fft(int skip, int dump, int low, int high, double threshold)
im += skip;
n -= skip;
res = malloc(n*sizeof(double));
out = malloc(n/split*sizeof(double));
if (!out) {
perror("malloc");
exit(1);
}
res = malloc(n/split*sizeof(double));
if (!res) {
perror("malloc");
exit(1);
}
switch (alg) {
case 0:
fft_complex(n, re, im, res);
break;
case 1:
fft_real(n, re, im, res);
break;
default:
abort();
for (i = 0; i != n/split; i++)
res[i] = 0;
off = 0;
for (i = 0; i != split; i++) {
switch (alg) {
case 0:
fft_complex(n/split, re+off, im+off, out);
break;
case 1:
fft_real(n/split, re+off, im+off, out);
break;
default:
abort();
}
for (j = 0; j != n/split; j++)
res[j] += out[j];
off += n/split;
}
for (i = 0; i != n/split; i++)
res[i] /= split;
if (dump) {
for (i = 0; i < n; i += 1)
for (i = 0; i != n/split; i++)
printf("%d %g\n", i,
10*log(res[(i+n/2) % n])/log(10));
10*log(res[(i+(n/split)/2) % (n/split)])/log(10));
} else {
/* @@@ need to think about supporting averaged FFT here later */
double s = 0;
double db;
@ -189,11 +208,12 @@ static void usage(const char *name)
{
fprintf(stderr,
"usage: %s [-s skip] [-w window] low high [threshold]\n"
" %s [-s skip] [-w window] -d\n\n"
" %s [-s skip] [-w window] -d [split]\n\n"
" threshold only use frequency bins with at least this power, in - dB.\n"
" E.g., a threshold value of 60 would be -60 dB. (default: %d\n"
" dB)\n"
" -d dump frequency-domain \n"
" -d [split] dump frequency-domain, optionally splitting the samples into\n"
" several parts and averaging over them.\n"
" -s skip skip this number of samples from the beginning (default: 0)\n"
" -w window use the specified window function. Available: blackman, hann,\n"
" hamming, rectangle. Default is rectangle.\n"
@ -240,7 +260,12 @@ int main(int argc, char **argv)
case 0:
if (!dump)
usage(*argv);
do_fft(skip, 1, 0, 0, 0);
do_fft(skip, 1, 0, 0, 0, 1);
break;
case 1:
if (!dump)
usage(*argv);
do_fft(skip, 1, 0, 0, 0, atoi(argv[optind]));
break;
case 3:
threshold = -atof(argv[optind+2]);
@ -252,7 +277,7 @@ int main(int argc, char **argv)
high = atoi(argv[optind+1]);
if (low > high)
usage(*argv);
do_fft(skip, 0, low, high, threshold);
do_fft(skip, 0, low, high, threshold, 1);
break;
default:
usage(*argv);