Graphical representations of the frequency response of a linear system
Frequency analysis of continuous systems

The frequency response T (jω) is a complex number that can be decomposed into a modulus and an argument:

T (jω) = A (ω) exp jφ(ω)

with $A\left(\omega \right)=\left|T\left(j\omega \right)\right|$

and φ (ω) = arg T (jω).

Knowledge of A (ω) and φ (ω) allows us to fully characterize T (jω), and therefore the system as we saw earlier (§ 2.2).

As in general, A (ω) is a decreasing function of ω; we usually speak of attenuation instead of modulus. The argument is also most often referred to as phase, and the curves representing...