function fft_filter, x, N_points, high_pass = high_pass

ft = fft(x, -1)

N = n_elements(x)

N_p = N_points < (N/2-1)

	if keyword_set (high_pass) then begin
ft(0:N_p) = 0
ft(N-N_p-1:*) = 0Š	endif else ft(N_p:N-N_p-1) = 0

return, float(fft(ft, 1))

	end