Otherworldly is an apt word to describe Tuvan throat-singing. On Tuesday at the Rotunda, as the three members of Tuva's Alash gave deep voice to the first of a dozen numbers, listeners having their first live encounter with the Central Asian folk genre could be identified by their startled looks. Developed over centuries among the semi-nomadic herdsmen of Tuva, where they could sing to each other over long distances, the eerie vocalizations have long been a national passion in the land bordering southern Siberia.