A music loop is simply a repetative chord progression, going round and round – often building up for each round. Orchestral loops are often hard compressed and loud with less dynamics than a Main Theme or an Underscore ( Filmmusic ). Loops can be powerful as stingers or short background passages in commercials and Youtube videos etc. Loops are useful for a more direct and short impact. However, a filmscore, underscore or main theme is quite different. For underscores and cinematic themes search within those categories.