The strains of choral voices from the distant lands of Sweden and Venezuela will blend with the Mostly Mozart Festival Orchestra this August in symphonic choral masterworks by Mozart, Beethoven, and Fauré, and will ring through Avery Fisher Hall unaccompanied by orchestra in a cappella repertoire of their own choosing.

The Swedish Radio Choir began coming to these shores in the 1980s, under the guidance of its legendary leader, Eric Ericson. In those years the group was exemplary of the lean, trim, vibrato-less blend that has long been the hallmark of Nordic choral sound. For those who knew the choir in those years, it may come as a surprise to see that the group's a cappella set at Mostly Mozart will feature excerpts from the Rachmaninoff Liturgy of St. John Chrysostom — music that calls for the rich, dark tones of Russian Orthodox cathedral choirs.

"That is why we chose the Rachmaninoff pieces for this tour," says the choir's deputy planning manager, Arne Lundmark. "It shows the quality of the choir better than many other works. The choir has gone to a broader, more symphonic sound in recent years. This piece requires extremely accurate intonation, and our choir can lean on a strong a cappella tradition. It is a good mix for us of the lean, well-tuned Scandinavian style and the full, deep Russian sound. We decided this would be the piece to bring to the U.S. Also, the conductor is Latvian and knows Orthodox church music very, very well."

The conductor in question is Kaspars Putnins, who doubles as conductor of the Latvian Radio Choir and the Estonian National Male Choir. "He made his first performance with the choir in May, so he is quite new in this conductor family of ours," says Lundmark.

During Mostly Mozart, in addition to performing Rachmaninoff, the Swedish Radio Choir appears in the Beethoven marathon programs with excerpts from Beethoven's Mass in C major, and two concerts of the Fauré Requiem. All three works are part of Mostly Mozart's spiritual theme that features great sacred choral works of the past five centuries throughout the Festival.

Another choir joining in this celebration of the spirituality of music is headed this way from the Southern Hemisphere: the Schola Cantorum of Venezuela and its remarkable music director, Maria Guinand (referenced with affection on the Schola's Web site as "La Generale"). The Schola, celebrating its 40th anniversary this season, has been, since its founding, the heart and soul of a vibrant choral movement in Caracas that did not previously exist. "We are a big family, founded by Alberto Grau," says Guinand. "I was part of the first generation. When we travel, we are 55 [people]. At home in Caracas, we are 70. We split the group sometimes or even add more people or join other choirs to do major choral symphony works. We have a very good sense of teamwork."

The Schola appears at Mostly Mozart fresh from an engagement at the Barbican Centre in London, performing in John Adams' opera A Flowering Tree under his direction. "We premiered it in Vienna last year," says Guinand. "The choral parts were written for us." The group is used to collaborating with composers, most famously with Osvaldo Golijov in his groundbreaking La Pasión según San Marcos (The Passion According to St. Mark) — a work that seems to leave critics speechless and audiences shouting for more. As surely as a ballet is choreographed "on" an individual dancer, this work was composed "on" the Schola Cantorum de Venezuela. Golijov regularly acknowledges his debt to the singers and leadership of the Schola in giving the work its final form.

The Schola Cantorum was still a young organization when, in 1974, it received first-prize honors in Italy's Guido d'Arezzo choral competition. The Schola's reputation grew through its participation in international choral festivals, all the while building a large choral movement back home in Venezuela. In 1996 Helmuth Rilling of the Oregon Bach Festival requested the Schola for a collaboration with the young Golijov.

The success of this project brought Golijov a new commission from Rilling — a Passion in honor of the 2000 Bach Festival, with the Schola Cantorum de Venezuela as designated choir. "Osvaldo accepted, although it was a big challenge for him," says Guinand. And thus began a unique creative process involving extended trips to Caracas to work with the Schola as the piece took shape. "Osvaldo is a very good friend," says Guinand. "We know the piece so well; we know what he wants because we created it together with him. We would work four hours a day, trying to find sounds, colors, effects, movement, expressions, the style he had in mind. You cannot just write everything on paper. We were all the time dreaming of things and creating things."

The Pasión brought the Schola to a new level of artistic maturity and international attention. "We could not have foreseen what would come out of it," says Guinand. "It changed the focus of our artistic life. We are very grateful for that chance to be daring, to give it as much energy as we could from the very beginning — to be in the right place at the right time."

At Mostly Mozart, the Schola Cantorum will cover a lot of ground in a few days. Their a cappella program features Latin American composers and, from 17th-century Italy, Antonio Lotti's lovely Crucifixus, "a little jewel," says Guinand, and a sort of reference point for composers like Ginastera and Grau, who refer to the 17th-century masters in their contrapuntal technique. "A demanding program, yes," says Guinand. "The Mozart Requiem we have sung many times. For that we will focus on the clean, non-vibrato Renaissance sound that applies. And then a very full sound for Ginastera or Grau — and, of course, we must come to the more open vowels and colors for the popular sound needed by Osvaldo. When we finish the Golijov we need a couple of days to adjust vocally.

"The Schola is a very versatile group," she concludes. "We do literature from the Renaissance to the 20th century. We also love our own popular music. We understand the difference between the one and the other. For us there are no barriers."

Marcia Young is a radio host for WNYC-FM and the classical channels of Sirius Satellite Radio.