Pop music history is littered with mysteries, but few more confounding than Johnny Mathis’ inexhaustible popularity. Since the mid-’50s, he has successfully recorded and concertized, surviving musical trends—from the British Invasion to heavy metal—that short-circuited the careers of far more accomplished singers, including Sinatra, Fitzgerald, and Bennett. From 1956 onward, Mathis has recorded for Columbia, only breaking this lengthy tenure in the mid-’60s to accept a lucrative three-year contract with Mercury. The Global Masters is a two-disc, 24-song compilation of long-unavailable material from this period, selected by Mathis himself. The singer’s style is distinctive, if hardly agreeable—a mewling tenor afflicted with pitch problems, a gerbily vibrato, grotesque phrasing, and mushy diction. His repertoire favors mawkish, plushly orchestrated ballads that build to semi-operatic Big Finishes that strain his vocal resources to the limit. (Only four of the Global masters swing; Mathis is arguably the squarest black pop singer ever.) The rare tracks on which he subdues his tendencies to whimper and bellow—”Limehouse Blues,” “On a Clear Day,” “So Nice”—are blandly tolerable, but when he pours on the treacle and pulls out the stops, the results are campily catastrophic. “When You Wish Upon a Star” leaves one yearning for Jiminy Cricket, while the grandiose “Granada” would choke Olive Garden diners. “The Sweetheart Tree,” Henry Mancini and Johnny Mercer’s hapless attempt to clone “Moon River,” is cloying enough to induce diabetic seizures. It’s difficult to gauge the audience for this stuff, though apparently one exists. The Global Masters might serve as a Mother’s Day gift for people who still have scores to settle with their moms. Unconscionably, Columbia/Legacy has chosen to inflate the selling price by spreading 81 minutes of music over two CDs when, by deleting just one selection, all the material could have been contained on a single disc. I’d nominate “Bye Bye Barbara,” the first (and worst) track, for exclusion. This simpering, low-charting single, backed by what sounds like a lobotomized adolescent girl chorus, would be more suitably included as a nonprescription emetic in a Dr. Demento emergency kit.

—Joel E. Siegel