FFT amplitude and wave energy

Hi,

I have different sets of time series data (same length, N and at constant rate fs=1/dt) for different wave amplitude and wave frequency.

f=-fs/2:fs/(N-1):fs/2;

z=fftshift(fft(x,N)/N);

plot(f,abs(z));

I have found somewhere that the amplitude of the wave can be obtained by multiplying normalised wave amplitude 'z' by 2, is that correct? As I have seen in another site that normalisation is done to make the amplitude wrt to a sine wave of magnitude 1.

I need to compare the wave energy for those signals, how can that be obtained from the FFT for a time series data?

Thanks in advance,

Dharma

[Daniel M]

You only need to multiply by 2 if you're showing only the single sided spectrum.

Please state the equations to calculate wave energy of a discrete signal, and we can help you code it.