Born in Osnabrück, Klein began his musical training in piano and composition with his father who made a living as an organist.
After touring and concertizing for several years, he settled in New York City in 1883 where he became involved with managing the German Theatre on Madison Ave.
He also was an officer of New York's musical club The Tonkünstler Society founded in 1898 (along with colleagues like Leo Schulz, Edward Graef, and Louis Saar).
[2] In 1904 he founded the Dramatic Oratorio Society with Selma Kronold with the goal of producing musical dramas based on the bible.
Karl was a violin prodigy born in 1886 who studied in New York with Ovide Musin and Eugene Boegner, and in Europe with Ysaye, Arno Hilf,[4] and August Wilhelmj.