NOTE 1 – Gaussian noise is entirely defined by its time varying mean and by a covariance function of two instants. If the noise is stationary the mean is independent of time, the covariance becomes a correlation function depending only on the difference between the two instants considered and the knowledge of this correlation function is equivalent to that of the power spectral density.

NOTE 2 – Gaussian noise may be produced by a large number of independent pulses such that in any finite time interval each has a negligible value compared to that of the sum of the pulses.

NOTE 3 – In practice thermal noise, shot noise and quantum noise are gaussian noises.