Swiss double-bassists Daniel Studer and Peter K Frey have been working together as improvisers for 15 years – a milestone they celebrated by inviting a host of seasoned internationalists to perform in various different configurations, as documented on this double CD set. With the exception of American drummer Gerry Hemmingway – who contributes equal measures of subtlety and grit to a 21-minute trio session – all of the participants are European, and the music created falls squarely into the European free improv school: principally concerned with the nature and effects of sound through the studied and rigorous investigation of timbre and texture. Even the largest grouping here – a septet of twin basses, piano, violin, bass clarinet, electric guitar and cello – instinctively avoids any kind of melodic or metric clutter, instead opening up wide vistas of contemplation and restraint. At the heart of all of it sit Studer and Frey, patiently generating ideas like a low-end engine of creation manned by white-coated Zen monk technicians.