The vocal quartet Timbre occupies a territory that at first blush might be worrisome. Vocal ensembles likely strike many listeners as being of a Swingle Singers or Christmas caroler ilk. The presence of three of Europe's strongest improvisers - percussionist Fritz Hauser, bassist Joelle Leandre and saxophonist Urs Leimgruber - might make a very different and similarly mistaken suggestion of what the group's second recording is about. TIMBREplus is about beautiful, unusual music, sounds as fresh as they are potable.

The group was founded by the American-born singer Lauren Newton, who has moved from her relatively jazzy 1982 debut (also called Timbre but reissued as Filigree by Hatology) to working with the likes of Jon Rose, Anthony Braxton and several projects with Leandre (notably their exceptional 18 Colors on Leo). The quartet - with Elisabeth Tuchmann, Oskar Morth and Bertl Mutter - probably sounds closest to some of Luciano Berio's vocal compositions. The compositions are credited to all four, which would suggest improvisation though their close interactions sound scripted.

The disc is divided into three suites, one with each of the guests, two quartet pieces and a quintet with the singers and Leandre. The guest musicians are all generally voice-like on their instruments and find their places within, not behind or on top of, the vocalists. Leandre's contributions work best, perhaps because she too is a singer (although she sticks to playing here). It's an unusual piece of work, which contributes to, rather than masquerading, the strengths of the performances.