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Originally from Atlanta, Georgia, and a graduate of The Westminster Schools, Stumm studied at the Curtis Institute of Music in Philadelphia with the viola pedagogue Karen Tuttle. She also studied at the University of Pennsylvania, and earned her Master of Music degree from the Juilliard School in New York. Stumm now divides her time between activities in the United States and in Europe. She also studied with violist Nobuko Imai and cellist Steven Isserlis whom she met at the International Musicians Seminar at Prussia Cove. Stumm is outspoken in support of the viola's own identity as an instrument distinct from the violin.
Stumm was a prize winner at three competitions — first prize of the 2005 Primrose International Viola Competition, second prize at the International Competition in Geneva and the Vriendenkrans Concours of the Concertgebouw, Amsterdam in 2005. In 2006 she became the first viola player to win first prize of the Concert Artist Guild International Auditions in New York. Her recent performances include her Carnegie Hall recital debut, Kennedy Center debut in Washington, D.C. as well as performances at Alice Tully Hall, New York, the Wigmore Hall and St. John's, Smith Square, London and the Concertgebouw, Amsterdam, at the Sitka Festival in Alaska and the National Concert Hall of Panama. She has performed Don Quixote (a tone poem for cello, viola and orchestra by Richard Strauss) with conductor Yan-Pascal Tortellier at the Bridgewater Hall, Manchester and the Sage, Gateshead, and the Bartok Concerto with the Hamburger Sinfonikern in Berlin and the L'Orchestre du Chambre, Geneva. She has appeared in the Rising Stars Series of the Ravinia Festival, Chicago, at the Verbier Festival, Switzerland, and has been heard on BBC Radio 3, NPR, and the Dutch and German national radio networks. For the BBC, she performed in Scotland and at the Sage Gateshead's Festival of Russian Music, as well as two live Wigmore Hall performances. She made her BBC Proms debut in 2008, returning in 2009. She appeared on the cover of Symphony Magazine's January 2011 issue. In 2011 she spoke about the viola in a talk, "The Imperfect Instrument," at the TEDx Aldeburgh conference.
Stumm's collaborative partners have included members of the Beaux Arts Trio, Guaneri, Juilliard and Alban Berg Quartets, and the period ensemble L'Archibudelli. She was until late 2009 a member of the London-based Aronowitz Ensemble, BBC New Generation Artists and received a Borletti Buitoni Trust award in 2009. She participates regularly at the International Musicians Seminar in Cornwall, having performed in that festival's annual tour, and has spent a number of summers at the Marlboro Music Festival in Vermont. Other festival appearances include the Delft, Spoleto and Aldeburgh Festivals and the Kronberg Academy's Chamber Music Connects the World."
Her first disc for Naxos of virtuoso Italian works for viola was released in 2011. 
Her latest disc, Harold in Italy, of the Berlioz work with songs by Franz Liszt, will be released by Orchid Classics September 1, 2014.
Stumm is currently International Chair of Viola Studies at the Royal College of Music, London, and Artistic Director of the Ilumina Festival, which she founded in 2015.