Christa Ludwig, one of the more dramatically expressive singers of our time, returns to Ravinia this year for the first time in two decades. Though I haven't heard this German mezzo-soprano live in a while, her recent recordings reveal a still richly plummy voice--she's 63--that hasn't lost much of its luster with age. Her Ravinia soujourn includes tonight's performance of Mahler's Das Lied von der Erde (with tenor Gary Lakes, backed up by the Chicago Symphony under the baton of James Levine), a work that she's given the definitive interpretations of. But it's Schubert's song cycle Winterreise that promises to be the best example of the old-fashioned, quintessentially German technique she's so well schooled in. This set of songs--completed in 1828, the last year of Schubert's short life, when he was depressed and in poor health--shows his particular genius for marrying lyrical poetry and music. One of the trademarks of Schubert songs is that the piano accompaniment--the exquisite phrasing, the graceful figures--offers succinct, picturesque commentary; Levine will be Ludwig's pianist. Monday, 8 PM, Murray Theatre, Ravinia Festival, Green Bay and Lake Cook Rds., Highland Park; 728-4642 or 708-433-8800.