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.
Both original melodies and a melodic sample
Sample pack VYPR
Loop name Cymatics - VYPR West Coast Melody Loop 4 - 100 BPM C# Min