The singers in Anonymous 4 have discovered in their 16 years as a touring early-music vocal ensemble that fame has its pitfalls and that they are not always what one expects.

 "There's the problem of being identified with what we sing," said Marsha Genensky, one of the four singers in the group, which is best known for its performances of medieval sacred music but is expanding in other directions as well. "When we've gone to Spain, we've found that people don't believe that we're not nuns. Because how could we possibly sing this music if we're not nuns?" . . .

 As medieval music groups go, Anonymous 4 has always been a bit unusual. When the group was formed in 1986, taking its name from the scholarly designation for the unknown author of an important medieval treatise, Gregorian chant and early polyphony were performed almost exclusively by men. Men's voices, after all, were heard in public church services at the time this music was composed; women's voices were not.

 But Ms. Hellauer, the ensemble's musicologist, has pointed out that public services were only part of the picture: nuns in convents would have sung the music at their own services. The growing fascination with music of the abbess and composer Hildegard of Bingen over the last two decades has added weight to that assertion and, not surprisingly, Hildegard has had a prominent place in the group's repertory. So even though none of the Anonymous 4 singers have taken the veil in the cause of authenticity, they have been able to offer a historically grounded argument for their particular blend of timbres.
 

Success With Recordings

 That blend has also been resoundingly successful on recordings. The group performed for five years before they began recording for Harmonia Mundi France. But their debut disc, “An English Ladymass,” sold 40,000 copies within two months of its release in 1992, an extraordinary figure in a corner of the record industry where a disc that sells 15,000 copies is considered a hit. Since then sales of “English Ladymass” have topped 220,000, and the group has made a dozen more discs for Harmonia Mundi (as well as one for Sony Classical). Two years ago Harmonia Mundi announced that the group had sold a million recordings worldwide.

 In a way, Anonymous 4 uses a strategy from the pop world to promote its recordings. Its programs are rehearsed in concert before they are taken into the recording studio. Once the disc is released, they tour with a program based on it, sometimes alternating with programs that promote earlier recordings as well. Their concert on Sunday, for example is essentially a live rendering of their latest album, also called “La Bele Marie.” . . .

 In past years the group has expanded on the music in its programs by adding poetry and narration between selections, and probably will do that in the future. But for “La Bele Marie,” it is performing the music as it is, with no readings and no intermission. If there is a new twist it is that for the first time each singer takes a solo turn.

 For all its success, Anonymous 4 has not relaxed the rigor of its approach to programming and performances. The “Bele Marie” program, for example, was tried in several forms before the group recorded it. . . .

 “Every few years we’d try again, and then put it away,” Ms. Genensky said.

 “But the conductus really captivated us,” Ms. Hellauer said, “and we wanted to perform it with something other than organum.”

 What Ms. Hellauer and her colleagues settled on were songs by Northern French trouveres, the lyric poet-musicians of the era. Generally, these are songs of courtly love, but the ones Ms. Hellauer selected are venerations of Mary, couched in the courtly tradition. . . . 

 But finding the right balance wasn’t the end of the problems “La Bele Marie” presented. There was the question of medieval pronunciation, something the group considers in each of its projects. Research on pronunciation is Ms. Rose’s department, and in this case she had to worry not only about how to sing medieval French, but also about how Latin was pronounced in France. . . .
 
 Then there was the matter of the text in Perotin’s “Beata Viscera” . . . The group wanted to include it on purely musical grounds, But four of its seven verses include anti-Semitic references. They decided to drop those verses, noting the omission, for the sake of scholarly propriety, in their program notes.

 “This is something we’ve run into before, “ Ms. Hellauer said. “In the ‘St. Nicholas’ program, there were several pieces where we changed a word –  instead of saying ‘the Jew converted,’ we made it ‘the merchant converted.’ When we do that, we always document what we’ve done. But there are also many pieces that we have chosen tnot to sing at all, that you’ll never know about.” . . 

Singing Offensive Texts

 The singers will take up the issue again in early April when they are guests at Toni Morrison’s atelier program at Princeton University. More broadly, their subject will be early American spiritual, gospel and shape-note music, one of several new repertory areas for the group. Within it, they plan to offer a section on offensive texts and how to approach the revival of offensive art of the past.

 The prospect of Anonymous 4 singing 18th- and early-19th-century American music may seem odd, but it is part of the group’s gradual branching out. By the mid-1990's the singers were collaborating on Renaissance programs with Lionheart, an all-male vocal sextet. And in 1997 they sang their first contemporary work, Richard Einhorn’s “Voices of Light,” an inviting piece written as a soundtrack for Carl Dreyer’s 1928 film, “The Passion of Joan of Arc.” Anonymous 4 has performed the work in concert, with showings of the film, and has recorded it for Sony Classical. (The performance is also included on the Criterion Collection DVD of the Dreyer film.)

 “The decision to do ‘Voices of Light’ was unanimous,” Ms. Rose said. “Richard invited us to the studio and played us the film music, and there was no question about it.”

 Ms. Genensky added, “The writing wasn’t exactly medievalesque, but it used our kind of sound and our kind of feeling, so it felt very familiar to us.”

 “And,” Ms. Hellauer said, “he was as easy to work with as a dead composer.”

A Newcomer Fits In

 More living composers followed. The group has performed music by the English composer Sir John Tavener in a collaboration with the Chilingirian String Quartet, including a new work that will be included on an all-Tavener disc that they recorded in February for release early next year. Later this year they will tour with a Christmas program that includes Britten’s “Ceremony of Carols,” as well as some traditional British and Celtic Christmas music, which they plan to record with the early-music harpist Andrew Lawrence-King. The ensemble has also sung works by Steve Reich and  a score composed for them by Peter Maxwell Davies has just arrived.

 It is tempting, and logical, to ascribe some of the groups’s new endeavors – Celtic music and contemporary works particularly – to Ms. Horner, who joined Anonymous 4 in 1998, replacing Ruth Cunningham. Ms. Horner was born in Northern Ireland and pursued a career as a new-music singer in London until she moved to New York in 1996. In the two years before she joined Anonymous 4, she sang both contemporary and early music, As it turns out though, Ms. Horner’s experience merely fit a direction the ensemble was beginning to consider anyway. Exploring the Celtic repertory was a project of Ms. Genensky’s and Ms. Rose’s. And the group took its first steps toward new music, in the form of “Voices of Light,” a year before Ms. Horner joined.

 She appears, however, to have fit into the group easily. . . .

 “Vocally, it wasn’t a great leap from what I had been doing because my sound was never a big operatic sound. I didn’t use a lot of vibrato, my voice was not very heavy. And some composers had actually asked me to sing their music because I had an early-music sound, and they liked that. So it was an easy transition. And now I’ll be able to sing new music as well