Spotify has recently announced that it will be changing the way functional content is remunerated on the service.
Functional content is defined as: all non-music, non-spoken-word audio (eg: white noise, nature sounds, ambient sounds, sound effects, machine noises, etc). Please note that non-music, non-spoken-word audio is not considered functional content if it is part of a musical or spoken word album.
Any track considered as functional content must have a minimum track length of 2 minutes to count as a stream, in comparison to 30 seconds for all other tracks. One stream of functional content will be worth less than that of a musical track.
More information about this can be found here:
Spotify Modernizing the Royalty System.