FFT waveform scaling

[GregFreeman]

So this has been asked a few times.

[LV_Pro]

So you have an answer? If not, what is the question?

[GregFreeman]

It wouldnt let me edit my post from my computer and deleted half of it which was my question lol. Sorry for that confusion. Shouldn't my fft plot have the spike at 10 not 1000 or do I need to put on a scaling factor of .01 on the x axis? If so, why? I thought calculating df should take care of this.

[Darin.K · Accepted solution]

You do have a peak at 10, and also at 990 which corresponds to -10 Hz.  You can turn on the FFT shift to get the DC-centered graph.

[GregFreeman]

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@Darin.K wrote:

You do have a peak at 10, and also at 990 which corresponds to -10 Hz.  You can turn on the FFT shift to get the DC-centered graph.

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Well, that sure does make sense. I should have zoomed in...I thought it was at 0 and 1000. Thanks for the clarification.

[YANYUNMENG]

hi，I have got a trouble,I do not know what is mean to -500;please help me.

[ChrisStrykesAgain]

The -500 shifts the start point of the waveform. This is required because the shift parameter of the FFT function is set to true.

The following link explains the FFT function in detail:

http://zone.ni.com/reference/en-XX/help/371361K-01/lvanls/fft/