Two Rs and two Ls... because the singing is extra. Trrill is about florid passages, improvisatory underpinnings, staccato'd intuitions, and virtuosities even at their most ridiculous.
Trrill's aim is to rediscover, rescue, remaster, repitch, and recontextualize footage and recordings of the greatest singers in the old-school operatic tradition—works that are primarily in the public domain or excerpted and edited to fix incorrect speeds or tones or audio-visual synching.
Caveat: I'm biased in favor of #baritones and baritone literature, but if you want to learn even more about these singers, checkout this spreadsheet. Voice parts are separated by tabs: bit.ly/2W4qmE3