ASCEE/lasp
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Fixed scaling issue in FFT

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This commit is contained in:
Casper Jansen 2021-08-13 11:40:25 +02:00
parent 4c0f399505
commit c98b10b83a
1 changed files with 16 additions and 13 deletions
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11
lasp/c/lasp_ps.c
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@ -117,16 +117,19 @@ void PowerSpectra_compute(const PowerSpectra* ps,
TRACE(15,"fft done"); TRACE(15,"fft done");
/* Scale fft such that power is easily computed */ /* Scale fft such that power is easily computed
const c scale_fac = d_sqrt(2/win_pow)/nfft; * - Multiply power spectral density by 2 except at f=0 and f=fNq
* - Divide by energy of window function = nfft * window_power
* - .. sqrt(factors) because it is applied to output fft instead of psd */
const c scale_fac = d_sqrt(2/(nfft*win_pow));
cmat_scale(&fft_work,scale_fac); cmat_scale(&fft_work,scale_fac);
TRACE(15,"scale done"); TRACE(15,"scale done");
for(us i=0;i< nchannels;i++) { for(us i=0;i< nchannels;i++) {
/* Multiply DC term with 1/sqrt(2) */ /* Multiply DC term by 1/sqrt(2) */
*getcmatval(&fft_work,0,i) *= 1/d_sqrt(2.)+0*I; *getcmatval(&fft_work,0,i) *= 1/d_sqrt(2.)+0*I;
/* Multiply Nyquist term with 1/sqrt(2) */ /* Multiply Nyquist term by 1/sqrt(2) */
*getcmatval(&fft_work,nfft/2,i) *= 1/d_sqrt(2.)+0*I; *getcmatval(&fft_work,nfft/2,i) *= 1/d_sqrt(2.)+0*I;
} }
check_overflow_xmat(fft_work); check_overflow_xmat(fft_work);