I was very pleased to take part in the singing of five O antiphons this morning in my OF parish, so first some provisos to forestall correction (but please don't think me defensive; this is NLM and mistakes hardly ever go uncorrected). First, I'm aware that the O Antiphons are not part of Mass but rather part of Vespers. We don't have a Vespers service, so the choice is for Catholics to hear them in Mass or never. Second, I know that it makes no liturgical sense to hear them one after another when they are supposed to be sung one per day (and yet we all sing Come O Come Emmanuel as a hymn with no wild objections from people, and this follows the same structure). Third, I have a problem with idea that just any song can be sung at Mass so in principle I object to the idea of importing a snippets and compilations and sticking them in Mass, and yet: the O Antiphons have such a huge role in liturgical history that it strikes me as a tragic loss to just throw them out of Catholic experience simple because we can't make them fit perfectly within the modern stew.
All that said, I just adore the O Antiphons. They are far more difficult than I imagined. They don't sound difficult. But I pulled them out only a few days ago with the intention of singing them and I was amazed at how easy it is to make mistakes. I ended up spending far more time practicing them than I expected. The words are unfamiliar and each has the same structure but with different variations for each unmetered text. The edition I was singing from (Liber Usualis) has many subtleties with surprising expressive notes and tricks throughout. The text itself is preeminent and must be proclaimed as a real announcement, so there is no room for slurring around or being vague about what you are doing. The melody is so completely structured around the need to proclaim that precise text.
I was also struck by how this must have originated in an improvisation within a broad structure, and yet here I was being super fussy about every marking. The editions of this piece across many orders of monks are very different, and I have no idea how Solesmes came up with the edition that is printed. But what choice do we have but to sing it exactly as it is printed. Hardly anyone has time to figure out what is essential and what is just a flourish.
Here are two editions of O Radix Jesse: