Multi-instrumentalist Burnt Friedman and drummer Jaki Liebezeit (a founding member of Krautrock innovators Can) have been working together since 2000 on musical projects that have gradually emerged as numbered releases under the title Secret Rhythms. The fourth volume in the series consists of six instrumental tracks ranging in length from four to nearly 16 minutes, all having random-looking numerical titles. Some are based loosely on material heard on previous volumes, but most of the music is new, and two tracks also feature guitarist Joseph Suchy (a regular guest on Secret Rhythms releases). Because Liebezeit and Friedman like to alter their instruments' outputs both during performance and in post-production, it's frequently difficult or impossible to tell what is being played, let alone by whom: are those really steel pans on "204-07," or is it just Suchy's guitar? "128-05" sounds like it consists entirely of percussion sounds, but who knows for certain? Ultimately, it doesn't really matter that much; this is relentlessly weird music, but also consistently lovely; it would almost be recommendable as relaxation or meditation music, except that it's kind of difficult to relax in 7/8 and 5/8 time. It might pass for trance music except that the textures shift a bit too often. Not only that, but Friedman and Liebezeit have an almost uncanny ability to produce music that is simultaneously quiet and unsettled, jittery and calm. Those who are looking for something between Brian Eno's Ambient series and Byrne and Eno's My Life in the Bush of Ghosts may find that this is exactly what the doctor ordered.