The first time you hear changjak gugak, you may reach for the wrong reference: this sounds like film music. That instinct is not wrong. Hwang Byungki's 1974 gayageum solo Chimhyangmu retains the traditional Korean left-hand vibrato (nonghyeon) and pull-plucks (tteudeum), but its melodic lines stretch over the long, abstract arcs that Western cinema scoring made familiar. Jung Jae-il's soundtrack for Bong Joon-ho's Parasite (2019) lives on that same continuum. Ensembles range from solo gayageum through five-piece chamber groups (gayageum, geomungo, daegeum, haegeum, janggu) to the fifty-strong National Orchestra of Korea (founded 1995). Traditional janggan (rhythmic cycles) sit under complex added meters. Compared to Japanese gendai hōgaku, the harmonic writing is softer: fluid slides from Korean pentatonic into second-and-fourth clusters, rather than confrontational atonality.

The starting point is 1962, when Hwang Byungki (1936-2018), a Seoul National University law graduate and self-taught gayageum player, wrote his solo Sup (Forest). Hwang's discipline was to keep the traditional scale system intact while borrowing modern Western sense of formal construction. The decisive work is his 1974 Chimhyangmu ('Deep-Fragrance Dance'), a meditation on the swirling smoke of Buddhist incense, which effectively named the genre. Institutionally, Seoul National University opened a Korean-traditional-music department in 1965, and the National Orchestra of Korea was founded in 1995 as a state-supported changjak-gugak ensemble under the National Theater. In the 2010s Jung Jae-il's scores for Parasite and Squid Game (2021) delivered this sound to a global audience of hundreds of millions.

First, the gayageum's left-hand vibrato (nonghyeon): sustained tones are held far longer than in Western string playing, the left hand continuously pressing and bending the string. Second, listen for traditional janggan cycles (jungmori, jajinmori) hidden inside irregular meters — the composer has usually reshaped them but not thrown them out. Third, the gayageum/daegeum contrast: plucked strings that decay, versus a flute that can sustain, is the basic sonic axis of changjak gugak. Fourth, in the Jung Jae-il era, Korean traditional lines are typically layered over Western string chamber ensembles and subtle electronic bass — the compositional world of contemporary film scoring.

Begin with Hwang Byungki's Chimhyangmu (1974); his own 1978 recording at the National Museum of Korea remains the reference. Then the Parasite (2019) original soundtrack shows how far the genre has travelled internationally. For deeper listening: the Hwang Byungki collected works (EMI Korea, 5 CDs), Kim Suk-cheol's soundtrack to Sopyonje (1993), and the National Orchestra of Korea's subscription recordings.

Hwang once said of himself that he was 'trained first as a lawyer, only later as a musician,' and critics have linked the almost architectural precision of Chimhyangmu to that legal-analytical training. His Seoul National University law-school class also included the future president Roh Moo-hyun. Jung Jae-il's route to changjak gugak is unusual: he started as a teenage jazz pianist, moved through K-pop production for Kim Kwang-jin and Lee Juck, and only then arrived at Bong Joon-ho — a trajectory that helps explain why his Parasite score reads as both traditional-Korean and mainstream-cinema at once.