Seismosoft | Earthquake Engineering Solutions

Hi,
What does it mean?
FourierAmpl(i)=sqrt[Re(i)^2+Im(i)^2]/df
I think it could be correct by this:
fft=sum(x[t]e^-iwt)

Hi
I read your answer but I could not undrestand your function?
please help me by write the fourier transform function in seismosignal clear such as MATLAB.
thanks