the 20th century a substantial repertoire was produced for the viola; many composers including Miklós Rózsa, Revol Bunin, Alfred Schnittke, Sofia Gubaidulina, Giya Kancheli and Krzysztof Penderecki, have written viola concertos. The American composer Morton Feldman wrote a series of works entitled The Viola in My Life, which feature concertante viola parts. In spectral music, the viola has been sought after because of its lower overtone partials that are more easily heard than on the violin. Spectral composers like Gérard Grisey, Tristan Murail, and Horațiu Rădulescu have written solo works for viola. Neo-Romantic, post-Modern composers have also written significant works for viola including Robin Holloway Viola Concerto op.56 and Sonata op.87, and Peter Seabourne a large five-movement work with piano, Pietà. Contemporary pop music The viola is sometimes used in contemporary popular music, mostly in the avant-garde. John Cale of The Velvet Underground used the viola, as do some modern groups such as alternative rock band 10,000 Maniacs, Imagine Dragons, folk duo John & Mary, British Sea Power and others. Jazz music has also seen its share of violists, from those used in string sections in the early 1900s to a handful of quartets and soloists emerging from the 1960s onward. It is quite unusual though, to use individual bowed string instruments in contemporary popular music. In folk music Although not as commonly used as the violin in folk music, the viola is nevertheless used by many folk musicians across the world. Extensive research into the historical and current use of the viola in folk music has been carried out by Dr. Lindsay Aitkenhead. Players in this genre include Eliza Carthy, Mary Ramsey, Helen Bell, and Nancy Kerr. Clarence "Gatemouth" Brown was the viola's most prominent exponent in the genre of blues. The viola is also an important accompaniment instrument in Slovakian, Hungarian and Romanian folk string band music, especially in Transylvania. Here the instrument has three strings tuned G3–D4–A3 (note that the A is an octave lower than found on the standard instrument), and the bridge is flattened with the instrument playing chords in a strongly rhythmic manner. In this usage, it is called a kontra or brácsa (pronounced "bra-cha", from German Bratsche, "viola"). Performers There are few well-known viola virtuoso soloists, perhaps because little virtuoso viola music was written before the twentieth century. Pre-twentieth century viola players of note include Carl Stamitz, Alessandro Rolla, Antonio Rolla, Chrétien Urhan,