Thanks for answering Mike. Here are my answers to some of your questions; below you will find a screenshot of the graphs:
The frequency graphs display on the x-axis the numbers from 0 to 6375 which does not correspond to the frequencies, because the sampling rate of the data is 1024 Hz, which would correspond to frequencies from 0 to 512 (if only half the data were plotted). Furthermore, since I am testing it using some EEG measurement apparatus, measuring nothing more than the 50 Hz buzz of the lamps, I should see the highest peak at 50 Hz and not at around 600. To make sure that my assumptions are correct, I wrote a short matlab script which plots an fft signal. I then loaded it into a mathscript node and let it run. You can see the result on the screenshot below. The 50 Hz are clearly present and also the 150 Hz and 250 Hz harmonics.
I will have to check to see if the data is formatted correctly, but I am pretty sure that it is.
Paul