More an exercise in performance art than a rock concert, Cat Power (the name used by singer Chan Marshall) took to the stage at I/O five days before Christmas and proceeded to test the resolve of even her most fervent fans. Cat Power's past few studio albums have been tour de forces of urban folk, true gifts to music. Live in Miami, Marshall stood alone and offhandedly strummed a guitar chord, intoned the opening words to a song, then came to a screeching halt. There were mumbling pleas to the soundman to turn her amplifier mix dramatically one way, then back again, until it was restored to its starting point. A wasted moment followed by another false start, more bantering with the increasingly dumbfounded soundman, and soon enough audience members began shifting from one foot to the other. They weren't dancing. Marshall plunked herself down at a piano and revealed a glimpse of what had drawn so many to hear her. Then it was back to the fumbling around and tuning problems. Less than an hour of this fulfilled her contractual obligations, and off she went, payment in hand. Equally inept, the audience was accepting, even though they left empty-handed.