Way to put FFT amplitude values in a vector

[lfoitek]

Hi,

I have an FFT of a sine wave and i am trying to get the amplitude values from the FFT into a vector.  I would like it to sample the amplitude values after the fundamental frequency has occured.

I've been looking at the property nodes for the FFT Graphs but i can't seem to get anything to work.  I attached my vi with the sine wave that would approx run for 2 seconds.  i would only need to take about 64 amplitude samples on the FFT, but if it was adjustable that would be best.

thank you

[altenbach]

Could you explain a little bit more about your experiment? Where is the real signal coming from. What determines the timing?

LabVIEW does not have vectors. Do you mean a simple 1D array?

Do you want the single highest amplitude from each transform or the amplitudes of all frequencies that exist in each transform (well, if your input really is a pure sine wave, there should be only one frequency, right? :))

Do you only want only the amplitudes or also their location (frequency)?

How does the VI know what the "fundamental frequency" is?

Instead of doing the transforms explicitly, you could just use "extract single tone information" on the original data for example, and grab the amplitude output only. Also, if you know the number of desired samples beforehand (and there is no need to be able to prematurely interrupt), use a FOR loop. Just autoindex the amplitudes at the right loop boundaries to form an array.

[lfoitek]

Thanks,
to clear things up a little.  i was thinking of doing simple word recognition.  i would sample about 2 seconds of sound, send it through a filter and then run an fft.  once i would get the initial spike in the fft (above a specific amplitude), i would store the sampled amplitudes in a 1 d array(not vector). 

if the frequency corresponding to the amplitude was possible that would be nice, or i could figure it out by the freq value at the inital spike and how many samples i take for 2 seconds.

thank you