On her 2008 self-titled release, bassist and vocalist Esperanza Spalding seemed to be gushing with music but at times the results were scattershot. 2010’s Chamber Music Society is a tighter affair and Spalding’s vocals, at times wordless, have a sharper sense of purpose. The core unit here — Spalding, drummer Terri Lyne Carrington, keyboardist Leo Genovese, and percussionist Quintino Cinalli — is joined by a string trio on a number of tracks. (Gil Goldstein collaborated with Spalding on the string arrangements and production.) The opener “Little Fly” effectively sets the words of a Walt Whitman poem to music for voice, bass, and string trio. “Chacarera,” based on the Argentinean rhythm, is full of clattering percussion, zigzagging vocal lines, and fine work from cellist Dave Eggar. Eggar also solos on an intriguing cover of “Wild Is the Wind,” which has nice melodica from Genovese. Special treat: the great Milton Nascimento joins Spalding for a vocal duet on “Apple Blossom.”