The words "free improvisation" inspire an elusive curiosity in some, while encouraging distrusting and annoyed grimaces from many others in the music community. Having roots in both free jazz and modern classical composition structure, the "genre" (or maybe, "set of techniques") seemingly continues where the modal jazz left off, that is trading even more harmony in for atonal structure. The movement values not so much the relationship between pitches and rhythms, but individual textures themselves.
Parker, Bailey, and Bennink's 1970 release on Incus records (the label's first) stands today as the most relevant and quintessential artifact of true, free improvisation. It's seemingly endless labyrinth of cymbal taps, guitar tappings, and saxophone buzzes provide an enigmatic map for listeners to follow, while struggling to find their way through the chaos. Evan Parker's solo work (which both mirrored American avant-garde pioneers such as Coltrane, while making them more abrasive), Derek Bailey's radical departure from traditional guitar technique, and Bennink's absurdist take on jazz percussion all culminate to create a monolithically landmark album. It can be challenging to listen to at first because it's object is to contain as little recognizable material/techniques as possible, but that doesn't mean it's unlistenable or unrewarding. Listen to it like your would a jazz album, and your mind will fill in the dots where the musicians suggest connections. It's extremely fidgety, disjointed, and unsettling at times, but once you get into the mode of listening to it, it'll challenge previous truths you held about rhythm, harmony, and song structure.