Standard deviation of the δS_ν distribution for all our models at all frequencies. Two simulation time-steps are shown: t = 102.7 Myr (higher transparency) and t = 184.7 Myr (no transparency). The first two panels correspond to the fresh injection model (ℳ_cr = 1 and ℳ_cr = 2.3 parameters), the third and fourth panels refer to the re-acceleration model, assuming a Dirac Delta pre-existing distribution function (γ_cut = 10² and γ_cut = 10³ parameters), and the fifth and sixth panels refer to the re-acceleration model assuming a power-law pre-existing distribution function (s = 2.25 and s = 3 parameters).