You listen to a master pianist play Chopin or Beethoven, and maybe, at least for 10 minutes after, you, too, an amateur, play with panache and speed and understanding you didn’t know you had. You watch Olympic figure skaters, and maybe, as an amateur skater, you skate brilliantly for a few minutes, in the flow like an Evan Lysacek.

Well, I’m telling you, the members of the Swedish Radio Choir, which sang Sunday afternoon at Hill Auditorium under University Musical Society auspices, are the Olympians of choral singing, and if every choral singer got a chance to hear them, the world might hum with gorgeous music for an awfully long time.

The magic didn’t stop in this concert of unaccompanied choral music, from the ethereal, angelic opening of Alfven’s “Aftonen” to the quiet, folkish close of the group’s second encore, an arrangement, also by Alfven, of the traditional “Uti vÃ¥r hage.” (The first encore was Alven’s “Jungfrun hon gÃ¥r i ringen.”)

The balances among the 32 voices in the choir are unimaginably perfect; ditto the phrasing, the purity of their sound, and last, but hardly least, their unerring intonation. This was Ann Arbor’s first chance to hear the Swedish Radio Choir at Hill in an cappella concert (they performed there in the Verdi Requiem in 2001), and on the occasion they were led by the expressive and graceful guest conductor Ragnar Bohlin, who has worked frequently with the choir in the past. The program was as fascinating and ear-opening as the singing was good. While it offered some Bach — the motet “Singet Dem Herrn" — it leaned more heavily on less well-known but equally amazing repertoire, including works by contemporary Swedish composers and an austerely beautiful mass for double chorus by the Swiss composer Frank Martin, from 1922.

Perhaps the most astonishing piece on the program was the wordless work that opened the second half, “Mouyayoum,” by Anders Hillborg, in which the singers, intoning sliding vowels, sound like instruments in some eerie celestial ochestra, sliding in on a whoosh of air from the void, occupying earth with their captivating babel, and exiting on another rush of air back to the void whence they came. It was mesmerizing — stunningly difficult, stunningly simple.

The parallels between works on the program were as interesting as the works themselves. For example, Sandstrom’s “Lobet den Herrn” takes its text from the Bach motet of the same title. But he employs double choir and joyous echo effects and repetitions, especially of the word “Lobet” (praise), that find their own happy echo in another J.S. Bach motet, “Singet dem Herrrn ein neues Lied” that followed “Lobet” on the program.

It was a pleasure to hear the very fine double-choir arrangement of Mahler’s “Ich bin der Welt abhanden gekommen” (by Clytus Gottwald), and to hear Rorem’s spikey “In Time of Pestilence.” But it was the choir itself that was the star of the afternoon , as well as the best repertoire this critic — and I wager a lot of others in the audience — never heard of before.