Composer Wayne Horvitz notes that he first invented these variations on his friend Butch Morris' ‘conduction’ methods to get the attention of ‘some high school hot shots’ who didn't like the collective-improv workshop he was running with them, but loved his fallback position. Horvitz invited them instead to assign numbers to groups of catchy motifs in one of his compositions, and react to them being called in random order by the conductor on the fly. The idea led Horvitz to form Seattle's Royal Room Collective Music Ensemble, and – for the 40th anniversary of Amsterdam's Bimhuis club in 2014 – this terrific pan-European version. The music crackles with ingeniously wayward but still cannily old-schoolish riffs, hauntingly harmonised, Carla Bley-reminiscent themes, jaunty swing hooks over crabbily lurching grooves – and constantly inventive individual and subgroup improvisation from a line-up of jazz-sharp experts who are equally well versed in post-1970s European free-improv. ‘Prepaid Funeral’ typifies the method, with its snappy short horn hook periodically punctuating surging reed-ensemble improvisations, low-end conversations for bass, trombone and baritone sax, and mid-range ones for clarinet and trumpet. The graceful ‘Trish’ testifies both to Horvitz' talent for memorable themes, and the bandmembers' close listening to each other. ‘Daylight’ starts on deep, didgeridoo-like sounds and winds up swinging; ‘Ironbound’ is a fanfare motif that invites a collective rumpus and ‘Forgiveness’ evokes Gil Evans and Ellington. Tightly-nailed section playing and unbuttoned improv could hardly be better balanced than on this fine set.