Any jazz artist, local or national, should feel privileged to play at this club in the 18th & Vine District. Musicians there don't have to worry about choking on cigarette smoke, and they can enjoy a sound system and a seating arrangement that keep the focus on the sound. The Blue Room, operated by the American Jazz Museum, has kept jazz alive in a part of town that for decades was musically silent. (Downbeat magazine has rated it one of the top 100 jazz clubs in the world.) Those accustomed to smoke and grit may have to work to adjust to the Blue Room's clean, museumlike décor, but after a few drinks -- and once the band starts -- patrons are transported to a time when Elvis Presley wasn't even a glint in his daddy's eye and Count Basie was baron of the barrelhouse.