When Per Norgard conceived A Light Hour in 1986, it was entirely improvised. In 2008, he and Ivan Hansen developed it into a fully composed and notated work. Each of its four movements has a basic character, and although a single tempo prevails almost from beginning to end, energy levels and subdivisions of the beat come and go.

I is slow and steady, with deep-sounding drums and ringing metallic instruments. II has fast subdivisions, an Afro-Cuban feel, and a much higher energy level, along with more varied percussion sounds. A different, often quirky set of instruments is heard in an Asian-tinged III, and Balinese sounds predominate in IV.

An hour-long work for percussion ensemble, built of systematic permutations of the same repeated pattern of two pitches—high-bright and low-dark—sounds like a prescription for tedium. That it is not is testimony to Per Nørgård’s mesmerizing rhythmic variety and percussionist/conductor/arranger Gert Mortensen’s colorful realization with the 22-member Percurama Percussion Ensemble. Though rigorously structured, this is not a work that easily leads you through its logic or even through a discernible emotional journey. Instead it seems to exist for the moment and presents patterns to be appreciated as they pass. This view is supported by booklet annotator Ivan Hansen, who assisted Nørgård in creating this version of the piece. In his notes, he relates Nørgård’s thoughts of writing a suite of pieces in which music of many styles and intensities would ebb and flow within a carefully developed structure, while audience, musicians, and perhaps dancers could come and go as the mood struck them. A Light Hour is, as he suggests, a piece that would fit into such a conception.

Nørgård created A Light Hour in 1986 as an hour-long improvisatory work for a group of amateur percussionists at a meditation center. Twenty-two years later he revisited the work, notating it for 10 or more percussionists, specifying percussion types in general—skin, metal, and wood—but leaving the actual instrumentation to the discretion of the performers. The organizing structure of the work is Nørgård’s “infinity series,” an aural equivalent of Mandelbrot fractals. Nørgård uses multiple layers of the same repeated four-measure pattern of two pitches, with high and low coinciding in the various layers, appearing at double or half the tempo of the other layers. The whole work reflects this symmetry, with four movements of approximately 15 minutes each, each divided into four subsections, which are divided into four smaller sections, etc. Each subsection provides the core material for the next three, and so on. Each section and subsection ends in a proportionally-sized “tone feast” based now on a four-pitch infinity series. Variety is provided by subtracting notes—“perforating” the line—changing stresses, and tying notes.

Every player uses a bright- and a dark-sounding instrument, and there are tuned percussion instruments that join in the “tone feasts.” Within the forms, improvisation is encouraged. Each section, as presented here, takes on a particular flavor. The first reminds one of traditional percussion ensemble fare: Aboriginal rhythms give way to jazz and rock, with a dizzying variety of styles explored as the simple beginning gives way to greater rhythmic and harmonic richness and ends in a dissonant roar of didgeridoos. Part II explores Afro-Cuban styles, with lots of drums—including steel ones—and potent bass. Part III turns to metal and wood in emore....