Digital filters can operate in the space domain by using the convolution product. A sampled signal can
be represented by a polynomial of variable z and/or by a set of coefficients. The convolution product of two
signals is the product of the polynomials in z domain of these signals. All linear filters can be presented
by the relationship between two polynomials in z.
A filter for whom the polynomial is a fraction, whose numerator is equal to 1, is an autoregressive filter or AR.
In this section, we study the behaviour of a second order AR filter. The second order AR filter is often used
as synthetic signal to compute synthetic seismograms.