The "roots music" of free jazz, and also its stereotype for many years. Pedal-to-the-metal, volume-set-to-11 blowing. Ascension and Albert Ayler, for instance. Sax players like Frank Wright, Charles Tyler, Peter Brotzmann, and David Murray used it as the starting point of their respective aesthetics, in most cases maturing into one more inclusive of jazz history, and of dynamics. It's always a fun place to visit, as John Zorn has done on occasion.