Two ensembles double the artistry in concert

CAMBRIDGE - Instead of opening its 13th season on its own, the adventurous early-music chorus Blue Heron played host to a newcomer. It was joined by Ensemble Plus Ultra, a British vocal group making its US debut. Each had a set to itself, and the two came together onstage to open and close a concert that spanned one century (the 16th) and two countries (England and Spain).

Hearing them side by side revealed fascinating contrasts. Ensemble Plus Ultra, directed by Michael Noone, is smaller than Blue Heron - eight singers to the latter’s 13. And Ensemble Plus Ultra assigns one singer to each vocal part, where Blue Heron will sometimes have more than one per vocal line.

This gives the British group a smaller, more focused sound than Blue Heron’s. Ensemble Plus Ultra doesn’t marshal the same kind of expressive daring that has won Blue Heron its reputation. But the group’s artistry is extraordinary in its own way: The singing was a model of precision and pure, willowy beauty.

This was heard to excellent effect in the second half of the program in a brace of works by Spanish composer Tomás Luis de Victoria, the 400th anniversary of whose death is being observed this year. This is familiar territory for Ensemble Plus Ultra, which has just released a mammoth 10-CD set of the composer’s works. In an eight-voice “Ave Maria,’’ Noone and his singers drew attention to a particularly biting dissonance in the score, and “Ave regina caelorum’’ was beautifully balanced and transparent. In three works for six voices, the singers worked without a conductor, the highlight of which was a translucent “Vadam et circuibo civitatem.’’

As for Blue Heron, it devoted its part of the concert to a single piece, “Salve regina,’’ a work of epic breadth by British composer Richard Pygott. One could hear the group’s familiar virtues: long, liquid phrasing, creative use of dynamics, and careful attention to the text. An exemplary moment: an explosion of florid sound near the end when the text describes Christ “pierced with thorns and fed with gall.’’

The groups sang together in three works that created a rich, fulsome sound despite a few rough, unsettled moments. In John Browne’s “O Maria salvatoris mater,’’ the full ensemble alternated with a series of duos and trios in which individual voices swirled together at close range. They closed with two Spanish works: Victoria’s buoyant “Laetatus sum’’ and Francisco Guerrero’s intimate “Duo seraphim.’’ Here’s hoping these two talented groups find occasion to work together again.