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usrp/fft.c: added Hamming, make dump easier to interpret

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- fft.c (window, fft_complex): added Hamming window function
- fft.c (do_fft): shift dump output such that center frequency is in the
  middle, not at the edges
This commit is contained in:
Werner Almesberger 2011-03-03 05:53:42 -03:00
parent 22f7eee195
commit fff1e1ed2f
1 changed files with 11 additions and 3 deletions
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14
usrp/fft.c
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@ -12,6 +12,12 @@
static int alg = 0; static int alg = 0;
static double window(int i, int n)
{
return 0.54-0.46*cos(M_PI*2*i/(n-1));
}
static void fft_complex(int n, const float *re, const float *im, double *res) static void fft_complex(int n, const float *re, const float *im, double *res)
{ {
fftw_complex *in, *out; fftw_complex *in, *out;
@ -23,8 +29,9 @@ static void fft_complex(int n, const float *re, const float *im, double *res)
out = fftw_malloc(sizeof(fftw_complex)*n); out = fftw_malloc(sizeof(fftw_complex)*n);
for (i = 0; i != n; i++) { for (i = 0; i != n; i++) {
in[i][0] = re[i]; double w = window(i, n);
in[i][1] = im[i]; in[i][0] = re[i]*w;
in[i][1] = im[i]*w;
} }
plan = fftw_plan_dft_1d(n, in, out, FFTW_FORWARD, FFTW_ESTIMATE); plan = fftw_plan_dft_1d(n, in, out, FFTW_FORWARD, FFTW_ESTIMATE);
@ -127,7 +134,8 @@ static void do_fft(int skip, int dump, int low, int high, double threshold)
if (dump) { if (dump) {
for (i = 0; i < n; i += 1) for (i = 0; i < n; i += 1)
printf("%d %g\n", i, 10*log(res[i])/log(10)); printf("%d %g\n", i,
10*log(res[(i+n/2) % n])/log(10));
} else { } else {
double s = 0; double s = 0;
double db; double db;