FFT with changing sample size

[ouhaoran]

I have been building several VI's to compute the power spectrum of an incoming signal. I would like to try something more advanced, but I honestly don't know where to start.

What I would like to do is to take a window of the incoming signal -- say 5ms @40000samples/second for 200 samples -- and compute the power spectrum first with 200 samples, then with 199, then with 198, ..., down to 190 samples and to compare these spectra. That is, the same 5ms chunk of signal, but each time doing the FFT with fewer samples.

I believe what I need to do is to create a custom window to use with the Adv. Signals FFT Periodogram, but I'm not certain of this. Any advice would be greatly appreciated as Google is proving unhelpful.

[johnsold]

I do not have the Adv. Signals VIs so I cannot comment on that.

The standard FFT.vi has a Size input.  Feed the same array in and reduce the size value.  You will need to read the help file to determine how it truncates the input array.

What are you trying to achieve by changing the number of samples in your FFT?  Maybe there is another approach.

Lynn