The last time Chan Marshall, the singer and songwriter who records under the name Cat Power, appeared in the area, the ratio of songs started to songs finished was about 2-to-1. That's better than average for her. Known for her onstage demeanor (a spellbinding collision of lacerating shyness and tantrum-ready frustration) as much as for her hypnotic albums, Marshall seems to court meltdown whenever she plays live. Supporting an all-covers album, her solo show three years ago at the Bottleneck was a grim sampler of the singer's most compelling and most risible qualities. Hiding under a veil of disheveled dark hair, Marshall complained bitterly about the sound mix and never heard the tone she wanted from her guitar, but the songs she managed to complete seemed to come from deep inside the same private oblivion in which her quiet, fragile albums gestate. The new Cat Power disc, You Are Free, picks up where 1998's Moon Pix left off -- in the dark, someplace the natives don't demand that their musicians tour. In what could be a boon to her performances or a sign of impending disaster, Marshall is supported this time by a band.