I am new to signal processing world. I am working on a project where we have to find change points using spectral densities. I am running some simulations where in I created a wave which is a linear combination of a few sinusoidals of frequency ranges (3.5-7.5, 7.5-9, 9-12, 12-14). I find the periodogram of these sinusoidals using the usual formula which goes from 0 to pi.
My understanding is, I will be able to observe peaks in the periodograms which corresponds to the frequencies of the signal. But since the x axis in a periodogram ranges only from -pi to pi, how can I compare my input frequencies and the frequencies I got in periodogram?