Small‐amplitude wave motion in a gravitationally stratified atmosphere permeated by a magnetic field consists, for each Fourier component with a certain frequency and horizontal wavenumber, of six quasiplane waves. Their mixture varies with height due to the continual interaction among these quasiplane waves. The simultaneous effects of compressibility, gravity, and a horizontal or a vertical magnetic field are shown by various wavenumber surfaces for decoupled plane waves.