Number of Samples in DAQ Assistant

[Cameroon]

Hi - I have a quick question:

I am using DAQ assistant and I am sampling at 1 kHz and I am reading 1000 samples. What my program does is perform an FFT on that signal. But my FFT size is 1024 (power of two) and I was just wondering if I should increase 'the number of samples read' to 1024 to make mathematical sense?

Basically I am wondering if those last 24 points the FFT  vi is reading are the correct ones. The reason I only take 1000 samples now is because I also do an autocorrelation and I only want 1000 points going into that VI.

Thanks

Cameron

[Justin D]

Cameron,

Are you using the standard FFT.vi?  If so then you don't have to specify a FFT size that's a power of 2.  You can just have an FFT size of 1000.  By default if you don't wire anything in to the FFT size terminal it sets the FFT size to be equal to the number of points in the signal that you send in.  If you specify a size of 1024 but only give it 1000 points, the FFT vi will pad the end of your signal with zeros which is probably not desired behavior for you.

Hope this helps,
Justin D.
Applications Engineer
National Instruments

[Cameroon]

Hi Justin-

Makes sense.Thanks