Trombonist and conceptualist John Rapson has been circulating on the fringes of the jazz scene for years, coming up with provocative new ideas in the vein of post-Mingus, post-AACM jazz. His latest project, a circuitous collaboration with Anthony Braxton, is something of milestone, and certainly one of the underrated albums of late. Rapson has long been concerned with balancing issues in his music-of finding new ways to cross-stitch improvisation and composition, intentionality and abandon. This time, Rapson inverted the usual route of improvising over preconceived compositions. Rapson sought out Braxton at Wesleyan University, recorded improvisations with him, took the DAT tape back home to Iowa, transcribed and re-composed parts from it. Rapson then brought out the charts and forms to a group of old comrades from Los Angeles-cornetist Bobby Bradford, tuba player Bill Roper (love that low to midling brass patina), drummer Alex Cline and keyboardist Wayne Peet-who flesh it out and add their own scruffy intellect. Rapson nods in homage to some musical heroes, as on “Libation: John Carter Amongst the Ancestors” and the final piece, “Oblation: Albert Testifies, Hildegard Prays,” bringing together the friendly ghosts of Ayler and von Bingen, at last. In all, it’s a concept yielding rich and unexpected results: a gospel-tinged, free-hinged celebration of jazz process and expression.