need help filtering a signal

[Philipp Schwaha]

hi!

what i need to do is fiter a signal to remove noise. what i wanted to try 
first was a fft then cut all frequencies except the the important ones (e.g 
100Hz, 200Hz ...), but when i did the fft i did not know how to do this, 
since there are no frequencies associated with the values the function fft 
returns. 
this is the first time i try to do something using an fft.
then i discovered the function fftfilter, but i could not make it produce the 
results i wanted.

how can i remove all frequencies from a certain signal, except a few selected 
ones?

thanks
philipp



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