  We consider the problem of sound propagation in a wind. We note that the
rays, as in the absence of a wind, are given by Fermat's principle and show how
to map them to the trajectories of a charged particle moving in a magnetic
field on a curved space. For the specific case of sound propagating in a
stratified atmosphere with a small wind speed we show that the corresponding
particle moves in a constant magnetic field on the hyperbolic plane. In this
way we give a simple `straightedge and compass' method to estimate the
intensity of sound upwind and downwind. We construct Mach envelopes for moving
sources. Finally, we relate the problem to that of finding null geodesics in a
squashed anti-de Sitter spacetime and discuss the $SO(3,1)\times \mathbb{R}$
symmetry of the problem from this point of view.
