Δ-variance spectra related to the models presented in Fig. 14. Each synthetic spectrum (blue triangles) is the average over 25 realizations of the maps with the same set of parameters. In all models, N_s = 300 and ψ = 2.5. The full line is the 1σ dispersion around the mean. The synthetic Δ-variance spectra are compared to that of the Cygnus-X North region and that of an fBm image with β = 2.4. In the grid of models, the best fit to the data of Cygnus North is for the case with ξ = −0.4 and η = −0.35.