In collaboration with the New York Times radio station in New York, WQXR, the music critic of the Times has pulled together some chatty monographs by contributing members of the WQXR staff--for middle-brow music appreciation. Among the explications and appreciations: opera (history, conductors, composers, what have you); orchestral, chamber music, choral music and the art song, etc.; the musical theatre, ""light music,"" jazz and folk music. Nights-in-Latin-America with Pru Devon (not as racy as it sounds) winds up. WQXR listeners will recognize the personalities and viewpoints. The unaffiliated will appreciate the free-style rambles. An ample and helpful discography illustrates the text. Extra whammy from the Times imprimatur.