Four of the UK's most accomplished creative music players incorporate for this live session of unbridled improvisation, transcending the limitations of conventional instruments. That's should be no surprise since soprano/tenor saxophonist John Butcher, pianist Pat Thomas, bassist Dominic Lash and drummer Steve Noble have been involved with sound expansion for decades.

Beginning with a spray of bullhorn-loud harsh projections from the tenor saxophone, Butcher's tone widens, pumps and throbs, soon joined by Thomas' pressurized clanks and clips, Lash's sul ponticello thrusts and Noble's sandpaper-like rubs and rebounds.

Noble's wobbling of unattached cymbals and hollowed drum pops, Thomas' keyboard swirls and processional comping and Lash's resonating string plucks are more than backdrops for Butcher's outbursts of aviary quacks, soprano sax whistles or squeezing out pure air without key movement. While thickened group expression is paramount during the CD's three tracks, space exists for trenchant solo interjections and division of the four into duo and trio configurations.

"Fathom Part 3", the pressurized final sequence, eventually reaches a climax that equally reflects light and darkness, sky high and basement pitches and varied tempos. As clenched bass string pressure stacks up against winnowing reed drones and drums rumbles against piano comping, the keyboard steadiness that Thomas has been consistently creating unperturbed throughout gradually relaxes the others timbral extravagances. A concluding blend of flat-line breathing from Butcher, speedy percussion rumbles and bottom string scrapes dissolves the program into stasis.

Prominent in solo settings and in numerous ensembles from duos to big bands, one can fathom that this collaborative improvisation creates some of the best work from these veteran players.