Nice article, again. Thanks! But two things I don’t get:

Philipp Sadler

121

In signal processing, the energy of a discrete signal *x[n] *is Σ|x[n]|² from *n=*0* *to* N-1*, where *N* is the number of samples. This computes the energy in the **time** domain.

Now, Parseval’s theorem states that the sum of the square of a function equals the sum of the square of its **transform**. Thus, you can calculate the energy in the **frequency** domain using this theorem. The energy of the signal equals (1/N)*Σ|X[k]|² from *k*=0 to *N-1*, where *X[k] *is the discrete Fourier transform of *x[n]*.