To celebrate his emancipation from the major-label system, E-40 released two albums simultaneously, comprising an astonishing total of 42 songs. The volume of material on the pair of Revenue Retrievin’ albums speaks to 40’s stamina and creative drive, but the consistency is what makes him an enduring artist. The unifying principle of these 42 tracks is bass — thunderous, unrelenting, magnificent bass. In the mid-‘90s E-40 was one of the primary architects of a Bay Area gangster-rap phenomenon known as “mob music,” and here he revives the bare-bones ferocity of that genre. The pairing of a sparse, stomping beat with 40’s twisty, unpredictable rhymes remains one of the great combinations in hip-hop culture. 40 gives guest spots to damn near all of the great Bay Area rappers, and the production duties are split between older masters — mainly the estimable Rick Rock — and a crop of younger beat makers that includes JHawk, Young L, and 40’s son Droop-E. Revenue Retrievin’ is one big smorgasbord of goodness. Jump in anywhere and enjoy — just make sure you play it loud, preferably in a moving car.