Charles Mingus has been a pioneer in jazz improvisation for about the last 20 years. As a bass player, Mingus has headed up numerous combinations, every one of them exploring free form in jazz. His performances this week, nightly at the jazz Workshop, will serve as a good indication of what everybody else will be playing five years from now. 733 Boylston St. nightly until Sunday. 8:30, 10:30 and 12:20.

Next doer, at Paul's Mail, tenor man Sonny Rollins will be playing at 8:30, 10:30 and 12:30. Rollins is the great myth of jazz. Even though he has not budged an inch from his already well-worn style of the early 60's, he is still one of the most revered musicans around His latest stuff is real disappointment for those who remember when he and Coltrane were vying for most innovative tenor. Shows no signs of coming around.

Sandy's jazz Revival on 54 Cabot St. in Beverly hosts jazz organist Wild Bill Davis and Count Basie's saxophonist Buddy Tate Through Saturday.