Thirty years ago an all-female folk choir set up in Bulgaria became the darling of Western audiences with its tradition-steeped a cappella singing, before the fall of communism threatened its survival. The Mystery Of The Bulgarian Voices ensemble conquered the international charts during the Cold War at a time when world music was beginning to gain popularity. Now the Grammy-winning choir from Sofia is back, having teamed up with Australian-born Lisa Gerrard of the music group, Dead Can Dance.