Recorded in Rotterdam in May 1970 and originally issued as a (now very scarce) vinyl LP on Misha Mengelberg and Han Bennink's ICP label, Groupcomposing was reissued on CD in 2012, but only as part of the limited-edition 54-CD box set marking the label's forty-fifth anniversary. Both of those options have become eye-wateringly expensive, so we must thank Corbett vs Dempsey for this CD release. As the personnel credit indicates, the septet that recorded this album was bursting with British, Dutch and German players who had a huge influence on the development of freely improvised music and are rightly described as 'legendary'. Dusting off the terminology of the time, the CD-cover-sticker quaintly refers to them as a 'free music supergroup'.

The music consists of two tracks, "Groupcomposing Part 1" and "Groupcomposing, Part 2", with lengths of eighteen-and-three-quarters minutes and twenty-three-and-three-quarters minutes, respectively, the split track and the durations revealing their origins as two sides of an LP. On CD, though, the transition is practically seamless, so the piece is effectively one extended improvisation. The use of "groupcomposing" in the track titles also hints at their vintage as, along with "instant composition" (as in ICP) or "spontaneous music" (as in SME), that term avoided the ambiguity of "free improvisation"; it would be some years until the term "improv" was commonly used. Away from the semantics, the music here is unquestionably improv as there is no evidence of pre-composed structures.

However, with seven players in the group, including four horns, there was clearly scope for overcrowding, leading to cacophony. That never happens here, indicating that there may have been some prior discussion about who would play when (but not what they would play). Throughout both pieces, the soundscape never sounds sparse, but never becomes so crowded that players get in each other's way or work against one another. Instead, they all manage to end up sounding as if they are fully tuned into the others' thought waves. There are countless examples here of individuals producing outstanding moments, but to pick out particular instances for attention would run counter to the overwhelming sense of this being a collective triumph. As much as Brotzmann's Machine Gun or SME's Karyobin, this album is an important landmark in the development of European improv.