Al Jarreau said he could “stay all night.” He almost did. Well, not quite. Jarreau, casual, relaxed, informal, affable, smiling a lot and utterly infused with music, seemed to be conjuring up his formative hang-loose, 1970s club gigs in Sausalito – he reflected on them very fondly – as he gracefully paced himself through the 13th Brubeck Festival’s headline concert Friday at Stockton’s half-full Bob Hope Theatre. “My 100-meter time’s the same,” Jarreau teased at one point. “But my distance running. …” Nevertheless, the 13-time Grammy Award-winning vocalist – he preferred “more R&B” than jazz as an adjective – vamped, scatted, joked, mused, occasionally slick-footed and generally grooved his way through a 13-“song” (depending on how that’s defined), 100-minute show. He’s like a one-voice Phish. A jam-man. Any direction’s good. A flexible, compatible, five-piece band backed up Jarreau’s percussive, improvisational inventions – providing him with occasions when he could rest on a stool, admiring them. He’s 74. Jarreau, who’s been doing this sort of thing for six decades, performed in the unfettered artistic spirit – anything goes – of pianist-composer Dave Brubeck (1920-2012), namesake of University of the Pacific’s Brubeck Institute. The concert and festival were dedicated to Iola Brubeck, an organizational, motivational and inspirational source of support during her 71-year marriage to Dave, an American jazz master and cultural ambassador. She died March 12 at age 90. Obviously, the years have added rough – occasionally fragile – contours to the smooth-jazz vocal stylings of Jarreau’s peak years. The grit and grind provided a slightly more-organic essence. Still, Jarreau reached for the falsetto-ish highs and dug into the droning depths, seeming to experiment with every phrase. Uttering whatever the moment might infer. That reached an apex when he and the band jammed through a lengthy – careening, colliding, chaotic – fusion of what seemed to be Brubeck’s “Take Five” and “Blue Rondo a la Turk.” Jarreau joyfully deployed his voice as a percussive instrument. He preceded that by orating an auctioneer’s-speed version of the lyrics Iola conceived for “Take Five,” saxophone player Paul Desmond’s familiar melody, a global standard since 1959.