The figures below offer additional depictions of aliasing, due to sampling. A graph of amplitude vs frequency (not time) for a single sinusoid at frequency 0.6 f s and some of its aliases at 0.4 f s, 1.4 f s, and 1.6 f s would look like the 4 black dots in Fig.3. The red lines depict the paths (loci) of the 4 dots if we were to adjust the frequency and amplitude of the sinusoid along the solid red segment (between f s /2 and f s). No matter what function we choose to change the amplitude vs frequency, the graph will exhibit symmetry between 0 and f s. Folding is often observed in practice when viewing the frequency spectrum of real-valued samples, such as Fig.4..