Behind all the great Motown sounds of the '60s (the Supremes, Marvin Gaye, Stevie Wonder, Smokey Robinson, and so on) was a pit full of musicians who paced each recording artist to the top of the charts. Paul Justman's soulful documentary traces the formation of the eclectic group known as the Funk Brothers and the relative anonymity they "enjoyed" while their sound was being splattered all over Top 40 radio. The film interweaves footage of the reunited still living Brothers performing Motown's timeless hits with such contemporary stars as Bootsy Collins, Joan Osborne, and Ben Harper; and Justman captures the essence of the politically tumultuous era without taking the bully pulpit -- this intimate portrayal remains focused on the musicians and their infectious music. (108 minutes) Opens Friday at the Flagship.