While analyzing the Doppler effect in everyday scenarios, a physics class discusses the behavior of a car's horn. Three potential effects are proposed: the horn's sound frequency appears higher when the car approaches due to wave compression; the sound seems lower when the car moves away owing to wave elongation; or the sound remains constant regardless of the car's motion as the Doppler effect does not affect sound perception. Which effect aligns with the Doppler effect's influence on the car's horn?