It’s hard to know exactly how much credit to give the Kronos Quartet for the recent expansion of interest in serious classical crossover recordings and for the renewed vigor in contemporary composition.  But it would be a mistake to underestimate the importance of this bold but well-marketed group of chamber whiz kids.

Well, they’re not “kids” any more.  The Kronos Quartet has been around for 32 years.  This reissue—though not their first recording—gets back to the roots of the group as young musicians in residence at Mills College where they met and began playing the music of genial maverick Terry Riley.  Kronos was dipping into rock and jazz as much as avant-garde classical music, so they must have found common ground with Mr. Riley, who was known for multi-hour piano improvisations as well as for his groundbreaking 1964 piece “In C”.  In the coming years, Kronos and Mr. Riley inspired each other, leading Riley to compose (for the first time) for the string quartet.  The results are here: four tonally consonant pieces in constant motion—beautiful music of a most wonderful, restless variety.

Terry Riley is usually touted as the “Father of Minimalism” or some-such, but that doesn’t get it right at all.  His music has been inspired by ragtime, raga and John Coltrane, and it doesn’t fit the “minimalist” mold so clearly established by composers such as Steve Reich and Phillip Glass.  Reich and Glass are best known for writing tonal, repetitive music that develops complexity and interest through movement in and out of phase, among other techniques.  The music here uses traditional tonality and repetition in places, but it is a world apart from the hypnotic loops of Reich and Glass.

Indeed, the centerpiece title track here, “Cadenza on the Night Plain”, has more in common with Coltrane’s “A Love Supreme” or Indian music than with any kind of phasing music.  Kronos plays long tones that bend in and out of pitch like an Indian stringed instrument—long pedal tones that evoke the open spaces of sky and plain—then they play carefully glissed and harmonized slides that suggest an American landscape—fiddle music of a sort, or Billie Holiday bending languorously into a perfect tone.  The story of “Cadenza” develops slowly, like a monologue taking its time to get going.  It’s a good eight minutes before the quartet begins to seem layered or contrapuntal, with competing voices moving in any traditional way.  But when that happens—with the piece acquiring a walking tempo in the cello that is not jazzy but is syncopated—the logic of the opening is clear: the various solo voices continue to slur and slide, but now in a dance that can be delicate, buttery or puckish.  A second slow phase is somewhat more atonal, but still a far cry from any kind of “minimalism”, with the music’s development very much linear and episodic, the repetition feeling much more like the harmonic patterns of jazz or pop music than the Tantric loops of Reich.

The other compositions are more accessible.  “Sunrise of the Planetary Dream Collector” features a nimble melody and driving figure in accompaniment.  When the second violin and viola move into a quickly repeating figure, it only briefly underlies short cello and violin solos that give way to a repetition that has a rock ‘n’ roll insistence.  In this music, however, the sense of groove is not hypnotic as much as playful.  “Sunrise” finds a half-dozen different ways to present its accompanying figure, but it is a fairly traditional kind of “theme and variations”, played with exceptional flexibility and expressive power by Kronos.

“In G” has the simplicity of Pachebel’s “Canon”—built from four chords played over a series of different counts (mostly a vigorous 6/8) and as zippy and pleasant as 20th Century classical is going to get.  The genius of it, I think, is how obvious it sounds at times—like music that must have always existed—but then how fresh and unnerving it can be the very next moment.  When Mr, Riley strips out the melody and just lets a figure repeat nakedly, it briefly suggests the mathematics and raw strength of what all music is at its core.  “Mythic Birds Waltz” is more programmatic and variable in its methods—moving from bird sounds to arpeggios to long struck “bagpipe”-sounding chords to swinging klezmer figures.

It’s not surprising that the career of the Kronos Quartet was boosted significantly by this outstanding recording.  Each instrument is sonically separable, but the group sound is strong and choir-like.  The music swings with great momentum and develops tremendous interest despite being written simply and transparently.  Kronos shows here the knack for playing quartet music the way Louis Armstrong played his trumpet—so that each measure, each note, is marked by a sense of individual expressiveness.

In later recordings, Kronos would take difficult, dissonant music and make it luminously easy to hear, but in this case the playing works the other way: bringing sensuous weight to music that might otherwise seem too easy to arrest your ear for an hour.