"The Unforgettable Glenn Miller." RCA. Swing music, popular in the '30s and '40s, certainly has more zing on '80s CD. There's not nearly as much of the background hiss and crackle that normally plagues old swing records and tapes. In particular, the cleaner sound adds considerable presence to trombonist/orchestra leader Miller's famed purring reed section. Miller, who died in 1944, was noted for songs like "In the Mood," "A String of Pearls" and "Tuxedo Junction," included in this 16-song, greatest-hits collection.