There's at least two reasons why the past two out of three albums by veteran pub rockers NRBQ have been live albums. First, in concert is where the band shines, the great songs befiting the ragged and loose glory of the quartet's live energy. Secondly (and this is just a guess), the venerable Rock & Roll virtuosos would rather be on the road than holed up in the studio. The group's current release, You Gotta Be Loose (Rounder), collects songs form various shows around America and exhibits that certain 'Q spark and humor that makes them one of Rock music's true gems. If you're a fan of NRBQ, you know all of this already. If you've yet to experience one of the band's shows, consider tonight baptism by fire, baby. Friday at Southgate House with Tim Krekel and the Groovebillys.