4. Process identification

A process is the set of phenomena forming a causal chain, i.e. ensuring the passage from an effect to its cause. In electronics, a filter is a system implementing a differential process between two time functions describing the input and output signals.

Identifying a process means determining the mathematical operation undergone by the quantities involved. In the case of a linear process, this means determining the system's transfer function, or its impulse response, which is its Fourier transform. In many cases, the information conveyed by the signal supplied by a system is not one or more parameters of the system's input signal, but its transfer function itself.