Indian classical music is ancient, codified, rigorous, and refined, yet its spirit dwells in the inspiration and personality of individuals. Because ragas are at once systematic — each is built on a signature ascending and descending scale — and improvised, every performance adds to the body of knowledge, yet no two are alike.
The great vocalists and instrumentalists are ones who bring grace, soul, and even surprise to this system, in a pursuit that can last a lifetime. Amjad Ali Khan, who plays the Berklee Performance Center Sunday night, is one of them. (He also leads a public workshop at the New England Conservatory on Sept. 16.)