Re: Is the output from an auto power spectrum complex valued?
Hello, It sounds like you've sorted out your questions through the two excellent response posts. I found a couple of knowledge base entries regarding FFT analysis in LabVIEW, and I thought you may want to reference them for further information/instruction. Please look at the following links. http://www.ni.com/support/labview/toolkits/analysis/analy3.htm http://digital.ni.com/public.nsf/3efedde4322fef19862567740067f3cc/eb86c3f027df072186256db0006c3612?OpenDocument I hope this helps. Please let me know if you still have any questions. Have a great day! Kind Regards, Joe Des Rosier National Instruments
Is the output from an auto power spectrum complex valued?
i want to display the fourier output of some ascii data that i saved to a text file. however the input to the FFT block must be complex valued.how am i to know what i see is actually the fourier analysis?please help
Re: Is the output from an auto power spectrum complex valued?
From a generic point of view the FFT operation input and output data are Complex. However since time signals are usually Real (like in your case), there is also a version of the FFT VI that takes Real input and produces Complex output data. Likewise there is a Inverse FFT (IFFT) VI that takes the Complex spectrum data as input and returns Real time signal data. In your case you should therefore use the Real FFT.vi located in the same palette. The output of your FFT being complex, you probably just want to display the Power Spectrum. To do so, convert your complex output to magnitude using the Complex to Polar primitive (numericcomplex palette), and square the r output to convert your magnitude r to a power signal. Note that there are additional scaling operations that are needed to get the correct result. So why not using the high-level VI located in your AnalyzeWaveform Measurement palette? The VI takes Real values waveform input and takes care of all needed scalings for you.
