The double bass is a perennial fixture of many jazz combos. And yet, how rare to hear it on its own terms. Rarer still in duet with a like partner. The Cornell Concert Series kicked off its spring season by proving that a duo of basses could be more than meets the ear. As twin ramparts of their generation, Christian McBride and Edgar Meyer are as masterful as they come. Where one cut his teeth on the jagged edges of jazz, the other was baptized in classical waters.