fft of short data length

I want to get frequency information of signal whose data length is not long enough (i.e. short).

However, if I use fft function and plot the results, it looked weird.

(It looks like they have two broken lines rather than round figure one.)

I think this is because the length of data is too short.

Is there any method or function that I can apply in this case?

Thanks.

Answer 1

[Matt J]

Yep. Zero-padding.

But realize that this will just give you more frequency samples, resulting in a smoother plot. It doesn't improve the accuracy of the FFT result as an approximation of the continuous Fourier Transform. Only finer sampling in the non-Fourier domain can do that.

[cldb0220]

Thank you so much! I'll try it!

[Adam]

The FFT will zero-pad for you though if you specify the FFT length (which I usually specify as next power of 2 up from my data length, but there are exceptions - for shorter signals I often go for longer than that.