Sometimes it can be heard loud and clear because its creator has been listening closely to an area's folkloric traditions, studying every detail. The ethnic "sound" is so obvious in Bartok, Kodaly, Janacek, Villa-Lobos, Revueltas that there's no need for a dissertation. It's there! Before them, composers who aspired to communicate this ethnic identity might not always have done justice to the "folk" because they either were disconnected or endeavored to ennoble the sound to such an extent as to divorce it from its humble origins (Chopin, Liszt, Brahms, Dvorak). And, then, there are all these "cultural areas" where that sound is not so distinct, so easily earmarked. For instance, what are the "folk" sounds of North Americans? Indian?! African-American?! British? French? Spanish? There were plenty of folk songs in French Canada, collected by Marius Barbeau, but how do these songs find their way into classical music? More pertinent to potential Scandinavian contributors, what's a Scandinavian "folk" sound? Is it discernible in the music of Carl Nielsen? Can it be clearly detached from Germanic influence in Grieg's works? Did Sibelius tap into the folkloric potential of northern Finland? Or did Grieg, Nielsen, Sibelius "construct" an entirely new sonic culture absolutely unrelated to popular music?
Why is folklore more easily detectable in some national classical music than in others?