Emil de Cou has been a productive and popular contributor to Washington-area music since his 2000-'03 term as National Symphony Orchestra associate conductor. Though he divides much of the year between his homes in San Francisco and Seattle, where he is the music director of the Pacific Northwest Ballet, he returns frequently to D.C. The NSO @ Wolf Trap Festival conductor also presents the orchestra's free summer concerts at Carter Barron Amphitheatre in Rock Creek Park.

As if de Cou were not sufficiently busy as a Smithsonian guest lecturer and preparing a multimedia production at the Seattle Opera House, he is music director of Virginia Chamber Orchestra. The ensemble's concert on Mother's Day marks the culmination of a project he has been working on for several years with musicologist Paul Meecham, president and CEO of the Baltimore Symphony Orchestra.

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"Paul, who is a Debussy scholar, brought to my attention an unfinished work by Debussy that he found on microfilm in New York City's Morgan Library," de Cou said. "The composer was in his early 20s when he wrote what appears to be a sketch for an early opera or cantata. It was orchestrated but never published."

"It's not clear if Debussy wrote it as an early opera or as a study before he began 'Pelleas et Melisande.' He sent it back to Theodore de Banville, a famous French poet, without indicating if he planned to do more with it. However, it's a very mature piece and you can hear the connection with 'Afternoon of a Faun.' About the same time, he wrote 'The Prodigal Son,' a beautiful cantata.' "

The "Diane Overture" receiving its world premiere Sunday was arranged for orchestra by de Cou and is connected thematically to "Diane au bois," the concert opera composed by Debussy for soprano, tenor and piano. Paul Meecham orchestrated "Diane au bois" for its U.S. premiere, also Sunday. A half-hour in length, it depicts Diana and Eros sitting on a rock. A flute solo followed by answering horns suggests a light, romantic comedy. Because Eros is in disguise, Diana does not recognize him and he is able to seduce her.

The soloists are soprano Emma McDermott and tenor Mauricio Miranda.

"This is the first time these two Debussy pieces have been heard together," de Cou said. "I've been working on this very exciting project for many years now and look forward to sharing these two Debussy premieres with today's music world."