The problem of acoustic radiation from a semi-infinite circular cylinder is discussed when a plane wave is propagated out of the mouth of the cylinder at which a vortex layer is attached. The effects of convection are included at low Mach numbers and a comparision is made of the radiation in the far field for the case of propagation in (a) still air, (b) moving air without a vortex layer and (c) moving air with a vortex layer. It is shown that in general the magnitude of the sound is much greater downstream than it is upstream. This directionality becomes more pronounced in case (b) than in case (a) whilst in the presence of a vortex layer the field is strengthened in the immediate region downstream and weakened elsewhere.