SF (dashed line) and its slope (continuous line) computed from a PSD shaped as a broken power-law, with α₁ = 1.2 and α₂ = 2, shown in the inset. The dotted lines indicate the values of the power-law exponent b, expected from Eq. (5) for the single power-law case, b₁ = 0.1, b₂ = 0.5. The cut-off in the SF at long τ is caused by the finite number of Fourier frequencies used in the FFT calculation. Time lags and Fourier frequencies are in arbitrary units.