India had a deep effect on American composer Philip Glass, who first became acutely aware of its music when he transcribed Ravi Shankar's film score for Conrad Rooks' Chappaqua for studio musicians in Paris in 1965-66. His encounters with this music on his first visit to India in 1966-67, and his initial encounters with the music of Morocco, Afghanistan, Iran, and Tibet on his visits that same year and later, had a huge impact on his subsequent work. It's all over Glass' nearly four-hour Music in 12 Parts (1971-74), which Glass and the current incarnation of his PGE will play for the first time on the West Coast at Davies Hall, presented by San Francisco Performances on Feb. 16. But does it sound Eastern? Judged from the two complete CD sets I have, it doesn't. Still, its focus on rhythm over harmony, its enlarged time scale, and the sense it gives of always being in a continuously unfolding present moment are deeply non-Western. Time is expanded and collapsed in this intense and complex piece.

Keeping 12 Parts together is Glass' music director and keyboardist Michael Riesman's job. How, I ask in a phone chat to his New York home, do his seven players negotiate this quick, demanding music, with its intricate polyrhythms and carefully layered textures? "Everybody listens to my left hand, which is the bass, because it's always playing the shortest note values, so everybody listens to that in their monitor." Do they have to rehearse a lot? "No," he says, "because we've played it several times in the last few years, in Amsterdam, in London and in Italy, so we know it. But it works best when it's tight and everything clicks in and feels right."

Some disparage Glass' music as dry, but I've always found it to be very emotional. Riesman agrees that even this piece, which is the culmination of Glass' reductivist Minimalist style, is emotional, noting that Part 1 is "very reflective," though he's way too smart to define it as being about this or that emotional state. But he does feel that it has a non-Western sense of time. "Philip always talks about the Indian influence, but from my perspective it's more like African music, which is very repetitive and rhythmic and has a ritualistic character. African music develops a groove and sticks to it."

Composer-wind player Jon Gibson, reached on his cell in New York, has a lot to say about 12 Parts, as well as his long working relationship with the PGE, which he joined in its first year, 1968, and has been a regular member of ever since. Does he find the piece ritualistic? "I think music for me is ritualistic, especially the PGE music, which is really structured, and this piece is almost like a Mass that way." He notes that hearing its 12 15-20-minute parts in succession, with a 60-minute dinner break between Parts 6 & 7, is "a 7-hour commitment" for the audience, "but they really go with it, and get it. We'll be playing practically nonstop the whole time. It requires a lot of concentration. It's a real challenge to play, but also very interesting to play. Parts 11 & 12 are very difficult to play, but when you get to Part 12, it's like, 'Yahoo!'"

Making it speak loud and clear is Dan Dryden's job. Dryden, who'll be doing the live sound mix and has been with the PGE since 1983, is very matter-of-fact about its challenges. "It's pretty straightforward because the ensemble is smaller – three keyboards, three winds, one soprano vocal – than in other pieces. But the problem is in maintaining the balance, especially when the winds play louder or softer so that people can hear all the parts. But the room will actually tell you what to do. You have to form a partnership with the room."

The latest and youngest member of the ensemble, composer David Crowell, who'll be playing winds along with fellow composer Andrew Sterman, joined the PGE in 2007, after he passed the audition test Riesman set for him, playing the rhythmic patterns in the granitic wall of sound which is Part 3. Crowell, reached at home in New York, describes it. "There are 12 figures in 4/4 in the first part in one key, and the 12 figures in the second part are in a different key. Each takes about 15 or 20 seconds, and you have to play them 15 or 20 times." But Crowell is obviously up to the challenges 12 Parts poses for its dedicated performers.

Philip Glass and the Philip Glass Ensemble, Music in 12 Parts, Mon., Feb. 16, 5 p.m., Davies Symphony Hall, SF. Tickets: (415) 392-2545; (415) 252-1937 (box meals), www.performances.org.