A set of parameters was developed to characterize the stress serrations produced by the Portevin-Le-Chatelier (PLC) effect, including the stress amplitudes and their frequency and time functions. In addition to the traditional Fast Fourier Transform (FFT), the Short Time Fourier Transform (STFT), which can simultaneously display the amplitude as function of time and frequency, proved to be very illustrative. This made it possible to identify type A and type B serrations, as well as their appearance in the spectrum. Based on this evaluation method, six different cold rolling and annealing variants of an AlMg3 alloy were analyzed. It was found that in the cold-formed and annealed versions of sheets an FFT amplitude peak uniformly appears at 4–10 Hz, which can be attributed to the PLC serration of type A. This peak continuously decreases in the case of the annealed sheets, while cold-formed sheet shows a new peak at approximately 18–20 Hz before the uniform strain, which indicates the appearance of type B serrations. The amplitude of stress serrations decreases with increasing yield strength, tensile strength and normal anisotropy, and increases with uniform and fracture strains and hardening exponent.