Lеt's say that i have a plot where i can see the spectrum of some discrete signal and let's say that it's x axis is normalized (by normalized i mean $\omega/\pi$ on the $x$ axis). Now, i know that in order to get to the real frequency at some particular point on the plot, i need to know the sampling frequency $f_s$ and then multiply that particular point with $f_s/2$ in order to get the actual frequency.
Now, i know this is maybe something trivial, but i am having struggle to understand why is this so, i mean, why multiplication by $f_s/2$ gives us the actual frequency in hertz?
Any help appreciated!