The Pittsburgh Camerata presented a concert of primarily a cappella Renaissance and 20th-century choral works Saturday at St. Andrew's Episcopal Church in Highland Park. Conducted by artistic director Rebecca Rollett, the 26-voice chamber choir exhibited excellent intonation, but its ensemble fabric was rent by the coarse soprano section.

The concert's focal point was the premiere of "Four River Songs" by Pittsburgh composer Nancy Galbraith: "The Mountain and the River" by Pablo Neruda, "The Negro Speaks of Rivers" by Langston Hughes, "the sky and a silver" by e.e. cummings and "Psalm 137: By the Waters of Babylon."

Galbraith's distinctive compositional language vaunts crisply rhythmic harmonic progressions complemented by lyric, accessible melodies. For these works, she added the full spectrum of choral textures, eliciting pithy expressions of the texts.

Galbraith's first major a cappella opus, "Four River Songs" exemplifies her versatility and insight. She filled the pieces with harmonic clusters, vocal ostinatos and complex counterpoint befitting the nimbleness of a chamber choir. The Camerata executed the sophisticated music adroitly.

The concert repeats at 8 p.m. Saturday at the Church of the Ascension in Oakland. Galbraith's compositions make it a must-hear.