Model power spectrum at λ = 3000 Å (solid blue line) for the parameters: M_BH = 2 × 10⁸ M_⊙, ṁ_Edd = 0.4, h = 20, Γ = 2, θ = 30°, α^* = 0, R_out = 5000R_g, E_cut = 150 keV, L_transf/L_disc = 0.5, and f_col = 1.7. The dashed red line and the dash-dotted green lines indicate the corresponding X-ray power spectrum, PSD_X(ν), and the normalised transfer function (multiplied by L_X, Edd² so that the product of the red and green line is equal to the blue line as Eq. (10) shows), respectively. The dashed red and vertical dash-dotted green lines show the position of the X-ray PSD break frequency and the transfer function break frequency, respectively.