In the previous sections we've been dealing with continuous (in s domain)
systems. Now we want to apply these systems to data so we will need first to discretize
to obtain a digital filter to then apply it to the data. Another typical
application is not to derive the filter from a model but design it from the
properties we want it to have (cut-off frequency, order, lowpass...).
Both topics will be covered here with two examples:

Obtain a digital filter from a model: we continue with the previous
closed loop example to translate the obtained models into filters.

Define filter properties: in this section we design a bandpass filter that will
allow us to estimate the noise spectrum of interferometer data in the desired
bandwidth.