The accuracy assessments of previous viscous/acoustic splitting methods (Shen & Sorenson 1999 and Slimon et al. 1999) have been made by comparing with DaNS (Direct Acoustic Numerical Simulation) solution for a dipole tone noise generated by Karman vortex shedding from a circular cylinder at M∞ = 0.3 and ReD = 200. The acoustic pressures are over-predicted by these methods and unexpected low frequency fluctuations are embedded. This is found not only due to the excessive generation of perturbed vorticity near and at the cylinder wall but also due to a lack of viscous diffusion term in their formulations. A modified formulation is proposed in the present study, based on the analysis of a perturbed vorticity transport equation. This equation shows a necessity of including the perturbed viscous stresses in the momentum equations to correctly handle the near field compressibility effect of wall-bounded shear flows. It also suggests a new perturbed energy equation, by which a flow noise at somewhat higher Mach numbers or a thermally driven flow noise at low Mach numbers can be handled. The present formulation yields both the far field acoustics and the compressible near field in excellent agreement with DaNS solutions.