Answer: I am pretty sure it is Ambient sound.
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Explanation:
Ambient sound is environmental sound or noise, background sounds appropriate to the physical space being depicted, such as crickets, water or birds. It extends the physical space, sometimes beyond what we can see in the frame. So, if you were writing music for a film and the location was in the woods, you would use things like birds chirping and leaves blowing in the air.
Hope this helps! :)
