Difference between FFT LabVIEW and Matlab FFT

Anyone know why there is a lag in the absolute levels of the results of the function in LabVIEW and Matlab FFT?

See the VI attached for an example of my code to LV.

Also attached is the plot generated in Matlab, which seems to be compensated by ~ 37dB.

This was generated by using the command "plot (10 * log10 (abs (fft (x))))", where x is the same as in the VI input array.

Thank you very much

Dan

I see you are using the VI of spectrum FFT which returns a unique range of face.  To convert a transformation both sides (IE FFT) in one spectrum sided with RMS units there is a standardization of sqrt (2) / n, where N is the number of points in x (t).  You can prémultiplier your x (t) by N/sqrt (2) and get the same results as Matlab.  Or, you can use the FFT.vi so you compare transform to transform instead of spectrum to transform.

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