1. Digital synthesis was used to make the spaceship sound alien and futuristic, but rapid mechanical movements were a reference to a car engine failing (since that’s a sound people can easily identify with). Gradual decrease in pitch emphasizes the ship’s descent.
2. Point of audition was used when the alien is evaluating his ship. The rhythmic alarm slowly transitioned to the rhythmic singing of a bird once his attention turned to the wildlife that surrounds him. When he returns to the realization that he’s stranded on a distant world, his ship’s alarm enters his mind again.
3. The sudden end of the ship’s alarm was to suggest a large passing of time and distance walked. If you could still hear the alarm off in the distance after the hard cut at 0:35 it would tell us he hadn’t traveled that far.
4. Background sounds changed dependent on location and time of day. The alien is outside of the city and in a wooded area immediately after the crash, so wildlife sounds were used much more aggressively. The further he traveled into the city the less birdcalls there were (although still prevalent due to how overgrown the city is). Insects suggested more of a displacement in time. The later the day grew the louder crickets were.
5. A lonely gust of wind was used at 0:55 to emphasize how empty the world is.
6. Diegetic sound was dropped out completely so music could take the lead during the montage sequence.