Fourier transform coefficients

[na1992]

I have a ser of a biomedical signals that I want to get their fourier transform coefficents and compare the coefficents. however when i use the FFT block in labview i only get the ooutput as a graph. is there a method for getting the coefficents of the fourtier transform?

[Bob_Schor]

Many people (such as yourself) ask for help, but don't show any code (making it difficult to suggest fixes).  The LabVIEW function FFT Spectrum (Mag-Phase) does output an array of Magnitudes (see below) and an array of Phases.  What are you doing?

Bob Schor

[johnsold]

The array of outputs of the FFT VI are the complex coefficients of the Fourier transform at the frequencies k*df.  Read the detailed help file for the VI.

Lynn

[na1992]

thanks for the reply this is whta i tried you mean the array is the coefficients??

[johnsold]

Yes.

Lynn

[Bob_Schor]

When you post code, post code, not a picture of code.  There are three ways to do this -- attach a VI, attach a ZIP file with VIs inside it, or attach (or insert as an image) a Snippet, prepared using the "Create Snippet from Selection" choice on the Edit menu.

You are using a different FFT function than I showed.  If I had your code, I could look at the function and tell you how to find out what it did.

I'm not sure what you mean by "Fourier Transform Coefficients".  If you have a Time series and you take its FFT, you get a Frequency series that you can use to "synthesize" your Time Series by adding sinusoids whose frequency, amplitude, and phase is given by the FFT.

Bob Schor

[na1992]

i have attached my vi and the two bocks im trying tou use for FFT but not sure which one is more suitabe for my purpose

i want to read the data file and then perform FFT to get the coefficents and categorize them into ranges to normal and abnormal signals.

i will than use IFFT to redraw the waveform of the data set using DAQ. my problem is how to get these coefficients from the FFT blocks ex: a, bn, ,,, ect

Thanks

[johnsold]

Please post a small data file with an example o0f your signal.  If the Forum will not let you post a .lvm file, change the extension to .txt or amke a zip file.

Lynn