Final answer:
The speed of sound in the atmosphere changes with a change in temperature, and although it changes when moving across different media, the frequency remains the same. Air pressure does not directly affect the speed of sound; it's the change in pressure that creates the sound wave.
Step-by-step explanation:
The speed of sound in the atmosphere primarily changes with a change in temperature, as temperature directly affects the density of the atmosphere, hence influencing the speed of sound. Although sound speed does change when traveling from one medium to another, the frequency of the sound typically remains constant regardless of the medium through which it is traveling. The frequency of a sound is determined by the sound's source and doesn't depend on the medium or the speed of the wave. Conversely, air pressure does not have a direct effect on sound speed; rather, it is the change in pressure that constitutes the sound wave itself.