ABC producers promised that the pop stars they recruited for this year's Super Bowl halftime show would do their singing liveâ??no lip-syncing allowed. But what about country star Shania Twain, who seemed to hop around the stage without missing a note?<P>Paul Liszewski, who produced the sound for the show, says Shania's mic was hot and her vocals were live. (Other audio engineers who watched the broadcast agreed.) Twain's accompaniment, however, was what's called a "band in a box," which means the back-up vocals and instrumentals we heard were prerecorded. So while the diva was belting out show-stoppers like "Man, I Feel Like a Woman," her onstage drummer was thrashing away merely for effect. <P> <BR>Other bands use a different mix of taped and live elements, depending on the nature of the show. At a dance-heavy concert where the lead singer does exhausting choreography, we might hear a tape of the lead vocal track. At an event like the Super Bowl, where sound engineers have five minutesâ??rather than the usual six or eight hoursâ??to set up, bands are more likely to rely on tape. During No Doubt and Sting's halftime sets, we were also hearing live vocals and canned instrumentals. Last year, when U2 played, we heard both Bono's voice and the Edge's guitar live, though the rhythm section was prerecorded.<BR>