An octet is bound to experience change over 40 years, and Roomful of Blues has seen a few new faces. A consistent sound is what holds its audience. A new singer like Phil Pemberton keeps things fresh, especially if nobody in the band writes songs. One trademark is the brisk exchange among guitar, trumpet and two saxophones, one of whom is senior member Rich Lataille. The Gatemouth Brown instrumental, “Gate Walks to Board,” tests the blues speedometer. “Win with Me Baby” has a Chris Vachon guitar solo to sustain a seductive mid-tempo waltz. Roomful of Blues has jump but is in no big rush, proof that busy performing bands should make a record now and then.