How does a band survive more than 20 years without a scratch on them or their discography? With Tortoise, some of that is due to the fact that its six members remain busy outside the fold: Guitarist Jeff Parker resides in LA, where his career as a jazz player thrives, and bassist Doug McCombs records on his own as Brokeback and with his other longtime band Eleventh Dream Day, to give but two examples. This allows everyone involved individual space and time to find new creative influences to bring back to the band. Once the sextet is together at last, the results are explosive and thrilling. That's the case with their latest album, The Catastrophist, a devilishly funky collection built from the stems of material the group wrote by a 2010 commission from the Chicago mayor's office to celebrate the city's storied jazz history. ROBERT HAM