If Tom Waits were to start a religion, it'd no doubt qualify as a cult. Although he's attracted a small but fervent group of adherents over the past two decades, his uniquely skewed amalgam of folk, blues, rock, and Tin Pan Alley standards has mostly escaped the notice of the wide world of mainstream music. That said, there's no need to preach to the converted: MULE VARIATIONS, Waits's first album of new material in six years, offers more of the gruffly evocative vocals, clanging rhythms, and angular instrumentation that have been his stock-in-trade since the release of his groundbreaking and influential 1983 work, SWORDFISHTROMBONES. This time around, Waits continues to break the rules and challenge the listener, not to mention his peers; this iconoclast's influence on other musicians is at once sweeping and subtle. But for those who scratch their heads at the found sounds, distorted vocals, and studio shenanigans that characterize Waits's work, it might help to think of him as a musical auteur -- songwriter, singer, and sonic sorcerer, an abstract expressionist who refuses to color within the lines. One never knows what will appear on the sonic canvas when Waits is through throwing paint, but it's always sure to be intriguing.