"Since 1982, Ensemble Organum has disrupted the early music scene with performances that have challenged audiences to listen to medieval music in new contexts. Directed by Marcel Pérès, the Ensemble draws from living chant and polyphonic traditions as well as from period sources to reimagine the sonic landscape of medieval music. Their 1996 recording of Guillaume de Machaut’s Messe de Notre Dame caused such a stir that critic Xavier Lacavalerie called the controversy the “Machaut affair.” For example, musicologist Andrew Kirkman claimed that the recording “smack[ed] more of the bazaar than the rarefied sound-world which most listeners [would] have come to associate with the performance of 14th-century western polyphony.” Other critics have described Organum’s unconventional style—influenced by traditional Corsican singing—as eastern, Arabic, or exotic, emphasizing the “distant” sonic world evoked by the recording. Despite these strong reactions, few have attempted to analyze their performance beyond surface-level description. In Chapter 1, I fill this lacuna by transcribing passages of Organum’s recording that best represent their use of Corsican ornamentation and timbres. I consider what Kirsten Yri calls “distancing features”—musical qualities that alienate the listener from Organum’s performance—drawing comparisons to Corsican music. To do so, I borrow from the ethnomusicological work of Caroline Bithell, who has documented this tradition in detail. Lastly, I show how Organum has established a new performance tradition, comparing how newer ensembles have followed in their footsteps. In Chapter 2, I place Organum’s recording within larger cultural trends, notably the globalist, postmodern aesthetics of the 1990s musical market—when medieval and world musics alike morphed from niche into mass phenomena. For example, plainchant albums like Chant and Vision became highly popular, topping the pop charts. Drawing on Johannes Fabian’s and Timothy Taylor’s work, I investigate how in the 1990s medieval and world music were often used to signify “the Other,” enabling listeners to rationalize their place in the world. By analyzing Organum’s performance practice and placing it in 1990s culture, I show how Organum’s rendition marked a milestone in the Mass’s recording history, still generating interest and controversy almost 30 years after its release."