Shivkumar Sharma and Zakir Hussain have both stretched the boundaries of northern India’s Hindustani classical music: Sharma almost single-handedly introduced a new instrument, a trapezoidal hammered dulcimer called the santoor, and Hussain continues to explore fusions with music from the West, as well as from elsewhere in his own country. In 1950, when Sharma first adopted the santoor–at the behest of his father, vocalist and tabla player Uma Dutt Sharma–it was unknown outside Kashmiri folk music. Purists deemed it unfit for interpreting ragas, largely because it couldn’t glide smoothly from note to note like the human voice; this kind of portamento, called meend, is vital to Hindustani instrumental music, which requires soloists to play with a singer’s fluidity. But by reducing the santoor’s complement of strings from around 100 to 87 and adding extra bridges–as well as by applying his own singular virtuosity, which includes a technique for moving seamlessly between notes by sliding his wooden strikers delicately along the strings–Sharma transcended the dulcimer’s limitations with authority. In 1968 he cemented the santoor’s legitimacy as a classical instrument with Call of the Valley, a recording with slide guitarist Brijbushan Kabra and bansuri flutist Hariprasad Chaurasia that went on to become one of the genre’s best-selling albums ever. Over the last couple decades Sharma, now 63, has forged an empathetic partnership with Hussain, a 50-year-old tabla master and son of Alla Rakha, Ravi Shankar’s preferred percussionist for many years; the two of them have appeared together on at least 11 albums. Hussain has also played in John McLaughlin’s group Shakti, which blended Hindustani classical, jazz, and south Indian Carnatic music; in Mickey Hart’s one-world all-percussion ensemble, Planet Drum; and on a hybrid drum ‘n’ bass project, Tabla Beat Science, with Bill Laswell and Talvin Singh. Fortunately his forays into world music haven’t dulled his edge as an interpreter of traditional ragas: he and Sharma strike sparks on Rag Rageshri (Moment!), trading intricate, lightning-quick embellishments of the piece’s theme. Friday, May 11, 8 PM, Simpson Theatre, Field Museum of Natural History, 1400 S. Lake Shore Dr.; 800-366-8332.