Dictionary:Signal-to-noise ratio (S/N)
The energy (or sometimes amplitude) of the signal divided by all remaining energy (noise) at the time. Sometimes the denominator is the total energy, that is, S/(S+N). Signal-to-noise ratio is difficult to determine in practice because of the difficulty in separating out the signal (the desired portion). Sometimes S2 is measured by a cross-correlation and (S+N)2 by an autocorrelation.