The base is original from the producer (chords and melodies), but is complemented with elements that complement the song that come from samplepacks, usually, vocal chops, guitars, wobbles sections, glitch effects. It is the standard in which most of producers work, in a project you will find MIDI files made by the producer, but also melodic loops.
3 bass layers
1 sub layer
8 percussion layers
5 melodic layers
Sample pack Black Octopus - Vocal Atmospheres by Cory Friesenhan
Loop name CFVA_Long_Atmosphere_Amin_03