BOSTON — At a time when more and more musicians are using music to purge their minds of personal grievances, Sarah McLachlan remains an anomaly, looking deeper into the human condition in an honest search for answers. Her new album, "Surfacing," may remind modern-day rockers that screeching guitars are no substitute for simplicity. McLachlan's songs are primal, often sketched only by the bare line of bass and drums - allowing her voice to weave freely between the strains of her sparse melodies. "Sweet Surrender" and "Witness" closely recall the intense unfulfilled longing that drove McLachlan's previous album, "Fumbling Towards Ecstasy." But "Angel" breaks new ground, showing a beauty and tenderness rarely seen in popular music today.