This idiom [Georgian traditional music] seemed as far removed from Bach’s glorious motet “Jesu, Meine Freude” as it did from 1960s works of Ligeti and Xenakis, all magnificently performed by the mixed chorus Ars Nova Copenhagen, conducted by the choral wizard Paul Hillier.

For the Bach, Mr. Hillier used 16 voices, unobtrusively supported by a portative organ, and you had the distinct sense that every voice counted. As usual, Mr. Hillier achieved marvels of balance and textual clarity that most choruses would envy but that was here, it seemed, only a starting point. A scintillating display of individualities and shifting emphases enlivened the performance at every moment.

The performances of Ligeti’s “Lux Aeterna” and Xenakis’s “Nuits” were no less accomplished. These are treacherous a cappella tours de force that you never want to hear an inferior chorus attempt. The Ligeti work, used in the film “2001: A Space Odyssey,” develops something of a paradox, a sort of static polyphony. It consists mainly of long-held notes by single singers entering periodically, generally within close pitch clusters but sometimes floating aloft, as if emanating from another planet; either way, finding the pitches requires intense concentration from the singers and in this case, at least for one, occasional help from a tuning fork.