The speed of sound in air (or mixtures of diatomic gasses) is a function of temperature only, independent of pressure and density. Or it depends on pressure and density in a way which cancels out and leaves only temperature as an independent variable for equivalent mixtures of gasses. (i.e. the speed of sound is the same at 20 atmospheres or 0.1 atmosphere as long as the temperature is the same) This becomes untrue when air is very very hot or very very cold, but generally those conditions aren't experienced on this planet outside of hot hypersonic flight.

Water vapor content, not being a diatomic gas does very slightly change the speed of sound but usually to a degree which can be ignored.

(people generally don't believe that the speed of sound in air depends only on temperature when you tell them)