how can I extract the frequency from the FFT function?

[Al-rawachy]

Hi All,

How can I extract the frequency from the FFT function in labview?  thanks in advance

Regards

[Bob_Schor]

If you put in a time series (usually by using a Waveform), you get out a frequency series.  Do you understand the concept of a Fourier Transform?  It involves taking a function of time and creating a function of frequency by doing certain integrals.  The FFT is just a "fast" numeric way of approximating this integral.  So the inputs will be assumed to be equally-spaced time points, and thus the output will be forced (by definition) to be equally-spaced frequency points. 

Bob Schor

[Al-rawachy]

Hi Bob,

Did you mean that, the df is the key to get the frequency?

[crossrulz · Accepted solution]

If you have the f0 and df, you can find your frequency just like you would find the time with a waveform based on t0 and dt.  You just need the index of the data point you want to get the frequency of.  The desired frequency is then f0+x*df, where x is the index of the data point you are interested in.

[Al-rawachy]

thank you, It's really helpful. thank you