Somehow, mariachi became synonymous with tourist trade Mexico. But in origin, it was a deeply rooted folk music of Mexico's poor, coalescing a century ago around the time the blues was born a little further north. Mariachi Real de San Diego reclaims that heritage, scouring thrift stores for scratchy old records and learning the old songs before they are forgotten. Their new CD, Mariachi Classics, is full of the old music's political fervor and lusty balladry, carried by brightly strummed strings and florid Latin horns and led by powerful, riveting vocals.