Noise power spectra used to reproduce the CMB experiments considered. We show the noise curves for Planck (dashed blue lines), SO (dash-dotted orange lines), and CMB-S4 (dotted green lines), as well as our fiducial 𝒞_ℓ for reference in black. Top, middle, and bottom panels: correspond, respectively, to the temperature, polarisation (we note the inflated noise at ℓ < 30 for the Planck-like case, cf. Sect. 3.3.1) and CMB lensing signals. Only auto-power spectra are shown, since we neglect the noise for the cross-correlation between CMB signals.