Deep into composer Terry Riley's newest disc,

The Cusp of Magic

- once your ears have been lulled by drums and rattles not usually heard outside of peyote rituals - you catch the unmistakable squeaking of a rubber duck. Riley laughs benevolently when, incredulous, you call that to his attention.

"It's part of the way I work," he said, speaking from his Oakland, Calif., home. "With each piece I write, I pick up different sounds along the way in this musical journey. And part of it was generated by David Harrington's toy collection."

OK, let's back up here.

The Cusp of Magic is a string quartet Riley wrote for his most frequent muse, the Kronos Quartet, one of three new works heading Philadelphia's way in the coming weeks. Parts of the Nonesuch CD are Riley's own version of Schumann's Scenes From Childhood, based on lullabies and cartoon-character music. Though it's hard to imagine Kronos' super-hip violinist David Harrington with kiddie toys, the fact is that he's a grandfather and tends to pick up things that squeak while on tour.

Though the California cutting edge may still look and sound youthful, it is increasingly eligible for Medicare - not to suggest any dulling of that edge. Since Lou Harrison's death, Riley, 72, is de facto dean of West Coast composers, which comes with an unofficial mandate to be a bit of a trickster, putting together combinations of people, music and sound that prompt audiences to contemplate deeper meanings in what may or may not be moments of playfulness.

That's really the only guidance on offer for the American Composers Orchestra concert at 7:30 tonight at the Annenberg Center, where Riley's Remember This O Mind will be heard just days after its New York world premiere. Or at Chamber Orchestra of Philadelphia's premiere of his triple concerto, Sol Terra Luna, for two guitars and violin, March 30-31 at the Kimmel Center's Perelman Theater.

Any given Riley work might involve Jack Kerouac text, a 108-beat rhythmic cycle taken from American Indian peyote rituals (in which Riley has participated), and perhaps a European fugue. The common denominator in all this is his spiritual life. Most composers have one, but few talk about it as frankly as Riley - a cornerstone figure in what was once a counterculture seeking enlightenment through hallucinogens.

Of music, he said, "It is a way of coming to know ourselves. For me, it's the best way. It doesn't have any dogma . . . or prescribed ritual, except in performing the music ourselves. By immersing ourselves deeply into music, we come to our spiritual nature."

And for him, that sometimes means taking a groove as far as possible, lending his music a lightness and an improvisational quality, even the massive orchestral work Jade Palace, a particularly extravagant 1990 Carnegie Hall commission that gives apoplexy to any conductor hoping to make each instrumental strand reasonably audible.

Similarly, Chamber Orchestra executive director Peter Gistelinck, commissioning the triple concerto, was cautioned by Riley's manager that the wait might be long. Instead, it arrived in two years (nothing in the classical music world) and at twice the prescribed length (40 minutes) with a somewhat sheepish explanation from the composer: "I don't know what happened to me."

Though more Eurocentric ears might hear Riley's works as outsized acts of dadaist eccentricity, they reflect a composer who has hit his peak creative years and accumulated the most singular pedigree in serious American music - partly because he has trafficked in areas that weren't so serious.

Riley first came to attention in 1964 with what's considered the minimalist movement's manifesto, the hour-long In C, which sought to strip music to its most essential basics. That and other works of this period not only influenced obvious figures - Philip Glass, Steve Reich - but prompted tangential followers such as the Who, the Soft Machine, Tangerine Dream and Curved Air. Riley also collaborated with John Cale, cofounder of seminal rock group the Velvet Underground, in the arty, respected album Church of Anthrax.

Work with raga vocalist Pandit Pran Nath took Riley in different directions in the 1970s, which brought him to Oakland's Mills College where he met Kronos' Harrington and developed a more personal style, suggesting mirages, hallucinations and unseen spirits.

"After I started moving away from so-called minimalism like in the Rainbow in Curved Air album, I lost some of my audience worldwide," Riley admits. "That happens. You can't get people to follow everything you do."

Other listeners' relationship with him began with 1983's Cadenza on the Night Plain, continuing through the two-hour string quartet Salome Dances for Peace, which he calls a "crossroads piece." Lots of works for traditional classical ensembles followed.

However, assuming that he has morphed into something different from his '60s self would be wrong. Again, he has a war to protest: The triple concerto's last movement is subtitled "Sarabande for Iraq."

"I'm pretty much the same person I was in the 1960s. And the world is similar now. . . . We're caught in a war we can't get out of, and facing the question of how to make peace in a world that doesn't seem to want it. In the '60s, idealism seemed to have a stronger thrust . . .," he says. "There was more hope. Maybe it's just taking longer for something to happen."

You ask if peyote rituals are still part of his life. He says no. He admits to having some interesting herbs in his garden, given to him by an Oklahoma medicine man, but they aren't there to be ingested. "The plants absorb the music," he explains, "and I absorb their vibes."

Contact music critic David Patrick Stearns at dstearns@phillynews.com.