A numerical study based on the macro-simulation method is carried out in order to determine the aerodynamical noise of a turbulent detaching flow. The macro-simulation method uses a Large Eddy Simulation (LES) code to obtain at the same time, the large structures of the flow and the small structures modelled by a sub-grid eddy viscosity, and an acoustic code able to calculate, in the far field, the radiated aerodynamical noises, from the Lighthill-Curle formalism. The method permits to dissociate the different aerodynamical noises: the wall noise, due to the wall-pressure fluctuations, the shear noise, due to the large scale quadrupole sources, and the turbulence self noise, generated by the small scale quadrupole sources. The case of the normal backward facing step is presented, for which the different emitted noises are analysed and compared together. Some theoretical hypotheses are also tested.