Output of RealFFT (VB.NET)

[Tweed]

Sorry if this question doesn't seem to make any sense but the object browser didn't provide much insight as to what is really being put into the Magnitude and Phase angle arrays after performing the RealFft(Double() as NationalInstruments.ComplexDouble).

Alright, so I followed the examples in the .NET examples that are provided with Measurement Studio in order to perform the RealFft on my collected data.

TempArray = Dsp.Transforms.RealFft(tempYArray)         NationalInstruments.ComplexDouble.DecomposeArrayPolar(TempArray, mag, phase)  
                                                                                               TempArray = NationalInstruments.ComplexDouble.ComposeArrayPolar(mag, phase)                   returnArray = Dsp.Transforms.InverseRealFft(TempArray)

Now what are the units for the values in the magnitude array. Is it dB or VRMS or ...

Again sorry if this doesn't make sense. I am VERY new to this type of analysis.

[Raj_V]

Hi Tweed,

The output of the RealFft function is dependant on the input values. If the input values are Volts, then the output will also be in Volts. The link below outlines the fundamentals of FFT analysis using LabVIEW and LabWindows/CVI. Although, it's not the same as .NET, the functions are comparable and may provide some insight into how they can be used.

http://zone.ni.com/devzone/cda/tut/p/id/4278