Abstract The present study is about the modulations of the aerodynamic broadband noise heard from slowly rotating rotors with few blades. It is aimed at producing a fast-running prediction tool that could be used to assess the nuisance of Vertical-Axis Wind Turbines (VAWT) in the context of urban installation. The simpler case of a skipping rope that only involves part of the modulation effect is addressed as a first step. The rope is split into segments for which an instantaneous sound-radiation model exists to yield an overall spectrogram. Finally, its time signature is reconstructed by additive synthesis. After inspection of existing databases from oscillatory-airfoil experiments, needs for data representative of the dynamic stall of VAWT blades are seen as the missing block to reconstruct a synthetic spectrogram.