Gravitational-wave observables for the intrinsic distribution of merging BBHs in the Universe for different formation channels according to the legends. Left: normalised chirp mass, ℳ, distributions where we can see that the PBH and GC channels leading to more massive BHs, whereas the maximum BH mass of CE and SMT channels is dictated by pulsational pair instability supernovae. Right: normalised effective spin parameter, χ, distributions where we see that only the CE channel generates a large ratio of positive χ due to tidal spin up, while both the GC and PBH channels lead to a symmetric distribution of χ (allowing for negative values) because of isotropically oriented spins in hierarchical mergers (GC) or uncorrelated spin growth (PBHs).