Celtic music means many things to many people. To some it recalls the Irish rebel songs of the Clancy Brothers, to others the ensemble playing of the Chieftains or Enya's ethereal vocals. Yet Celtic music is much more than reels, jigs, and sentimental ballads. It is also unaccompanied singing, feverish fiddle tunes, the sweet strains of the Irish uileann pipes. It comes not just from Ireland and Scotland but from Wales, Brittany, the Isle of Man,...