Reconstruct time series from FFT components. There is a time shift error.

Hello,

I'd like to extract various frequency components (amplitue, frequecny, phase) by applying FFT to a time series. Then to check if I get the correct numbers, reconstruct the time series by summing up the cosine components. As shown in the figure attached, there seems to be a growing time shift. What went wrong in my script? This issue is absent for my another set of data though.

Thank you!

Answer 1

[Paul]

Hi Haifei,

You may want to investigate why the data is not uniformly sampled and how that impacts the analysis. Does the other set of data exhibit the same behavior?

load fftData.mat

t = t_exp';
x = y_exp';

plot(diff(t))

[Haifei Chen]

Hi Paul,

Thank you for pointing that out. I didn't notice the samping rate is not strictly uniform for this dataset (it was uniform for the other dataset).

Much appreciated!

Haifei