Characteristic strain as a function of frequency for three different universe models (log₁₀A = −2, α = 0.3, β = 1, log₁₀M₀ = 8) featuring: circular GW-driven binaries (blue), circular but stellar+GW-driven binaries (ρ = 10⁴ M_⊙ pc⁻³, orange), and eccentric GW-driven binaries (e₀ = 0.99 at 5 × 10⁻¹² Hz, green). Thick lines denote the theoretical GWB, while shaded areas denote the 10th and 90th percentiles of the characteristic strain when different discrete realisations of the population are considered. The thin line of the same colour denotes one such realisation for each model.