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Janis Martin, Opera Star Who Stretched Her Range, Dies at 75

Ms. Martin, a mezzo-soprano who became a soprano, gained international recognition for her performances in Wagner and Strauss operas.
By DANIEL E. SLOTNIK, NYTimes...|...WIKIPEDIA
 Janis Martin (August 16, 1939 – December 13, 2014) was an American opera singer who sang leading roles first as a mezzo-soprano and later as a soprano in opera houses throughout Europe and the United States. She was particularly known for her performances in the operas of Richard Wagner and sang at the Bayreuth Festival from 1968 to 1997.