Sound does not travel in atmosphere straight-forwardly. Even in open spaces, it does not necessarily spread evenly to every direction. A silent wind without turbulences carries the soundwaves with it. The atmosphere also has a set of different layers that can reflect the upward-reaching waves back towards the ground.
In silence, the reach of sounds is wide. When the trees are silent and the wind is gentle, speech can travel from a top of the hill to another.