This paper presents a sound synthesis approach that allows investigating the noise annoyance of rotorcraft in relation to the source components and flight path. The sound synthesis is based on a source-transfer-receiver model, describing the noise emission and directivity of the sources and their propagation towards the receiver point on the ground. Several noise propagation effects are considered such as the Doppler shift, distance effect, atmospheric absorption, ground reflections and the effects of head and body. A case study is presented, showing the complete modeling and synthesis procedure for a four-bladed twin-engine helicopter. The source data was obtained from numerical simulations. Flyover sounds were synthesized for a baseline trajectory and a noise-optimized flight path.@en