YOUSSOU N’DOUR Nothing’s in Vain (Coono Du Reer) (Nonesuch) The Rough Guide to Youssou N’Dour & Etoile De Dakar (World Music Network)Senegal’s prodigal son has been called the world’s greatest pop vocalist. True or near true, nothing he’s recorded to date argues the case as convincingly as Nothing’s in Vain. Purring through his midrange, soaring to gentle highs, and exploring a wonderful but little-used lower register, he blends African, Middle Eastern, and European singing styles with an authority Sting can only dream of. The folksy, neo-acoustic arrangements (tres au courant in world-music circles) are energized by N’Dour’s chattering signature mbalax rhythms; New Age synths and postcolonial French pop corn occasionally lend an off scent, but this is mostly pure perfume. The dependable Rough Guide series, meanwhile, showcases some of N’Dour’s best home-brewed early sides; with fiery band in full swing, these snaky, lo-fi, Latin-tinged dance grooves deliver an even more kinetic pleasure. POP FLASHBACK The bubblegummy vamp that caps In Vain’s ”La Femme Est L’Avenir de L’Amour” (”Women Are the Future of Love”) sounds like a West African echo of a ’70s Voice of America broadcast.