Key among the achievements of the Kronos Quartet has been the exponential expansion of string quartet repertoire by commissioning new works far and wide. But it is the very far-and-wide aspect that accounts for their other notable success-bringing the voices of international composers into what has traditionally been a western classical organism. One such example is Chinese composer Tan Dun’s “Ghost Opera,” a fascinating ambi-cultural piece for string quartet and the Chinese lute called the pipa (played by Wu Man). It has just been released as one of the Kronos “singles” (Nonesuch; 35:46), consisting of single works on a CD. Dun’s work is operatic in the sense of seamlessly bringing together assorted emotive qualities and global cultural instincts: we hear snippets of Baroque, of traditional Chinese music and atonal sonic colors, as from a unique palette that knows no boundaries. Tying together east and west is a delicate process, failing more often than succeeding. But “Ghost Opera” succeeds, renewing hope in the prospect.