The Cambridge Singers will offer an extraordinary...

The Cambridge Singers will offer an extraordinary program of Russian church music, much of it rarely, if ever, heard in this country, during two concerts in Pasadena this weekend.

Pieces range from 11th-Century znomanny chants to songs composed by Ivan the Terrible to rarely performed hymns by pre-Bolshevik composers.

Russian liturgical music is, of course, as old as the Russian Orthodox Church itself, which most historians date to the baptism of Grand Prince Vladimir in AD 988.

The tradition is a rich and varied one, says Alexander Ruggieri, music director of the 45-member Cambridge Singers. Among its influences are the Greek and Bulgarian clerics who introduced chanting in medieval Russia, the Italian chapel masters who brought symphonic forms into the 18th Century, and the back-to-the-roots nationalism of late-19th-Century and early-20th-Century Russian composers.

But one thing remains constant: It is strictly music for the human voice.

“Only voices were said to be appropriate to praise God with understanding,” says Ruggieri, who is taking part in a massive effort to compile and publish the most important Russian liturgical music of the past 1,000 years.

The Los Angeles-based Cambridge Singers are known for their willingness to take on big challenges. Last year, they performed a Purcell opera and a Vaughan Williams cantata on the same program, and this year they unveiled a widely praised “Messiah.” Ruggieri has been the director since the choir’s beginning in 1984.

The weekend program, billed as “1,000 Years of Russian Choral Music,” will be performed at St. Anthony’s Greek Orthodox Church, 778 S. Rosemead Blvd., Saturday at 8 p.m. and Sunday at 4 p.m. Admission is $13.75. Information and reservations: (213) 484-1557.