Noise level as a function of H I recessional velocity for the 24″ tapered H I cube made for a typical MeerKAT 5 h observation. The median noise level is indicated by the dashed line. As discussed in Sault (1994), the noise increases in channels that are excluded from the visibility spectral fit described in Sect. 3.5 (in this case, two small H I velocity intervals centred at ∼900 and ∼1300 km s⁻¹).