Philip Glass opens his own door. He ushers me into the front room of his East Village brownstone — busy, unkempt and fully lived-in — to drop my coat off and wait a minute. I am, it seems, early, and Glass is still busy with his previous task. As I peel layers that protected me from a frosty New York afternoon, Glass shuffles into the next room over — the music room, it turns out — and gets back to quietly, intently banging out single notes on a piano. Let me tell you, there is no feeling like the feeling you get when you realize that you have accidentally interrupted Philip Glass — among the most influential American composers of the last century, one of the masters of contemporary classical music “with repetitive structures” (he shies away from the term “minimalist”), recipient of countless arts awards and lifetime-achievement medals — from working on music.

Glass has lived in this house since 1984, and that crowded room — grand piano, synthesizer, floor-to-ceiling bookshelves filling up much of its capacity, sheet music, art and Eastern artifacts on every surface — is where he does his composing. It is, in fact, the room where he wrote most of Symphony No. 11, which premiered at Carnegie Hall on January 31st, which also happened to be Glass’s 80th birthday, the overlapping hallmarks far from a coincidence.

“The whole thing was a set-up,” Glass says through a smirk that rarely disappears during our conversation, a couple of weeks after the event. “The people who work for me commissioned it to be done on my birthday which was going to take place at Carnegie Hall.” (He assumes a voice of faux-incredulity: “No pressure. ’Oh, I see, this is my party and I have to do the work?’”) Glass says he temporarily fretted the stressful circumstances — rewriting the symphony’s last 11 pages after the first rehearsal because “I realized that the ending was not definitive enough” — but estimates that the debut, performed by the Bruckner Orchestra Linz, under the direction of its chief conductor (and longtime Glass collaborator), Dennis Russell Davies, went over pretty well. “The reception seemed fairly authentic. People really did like it. They weren’t just applauding because I was 80, like you might see with [older] people out running in the park, and people go ‘Yay’ only because they can still do it.”

“My days of listening were connected to my father’s record store, where I began working when I was 12. My first job in the music world was advising people what records they should buy, so I had to know all the records in the store.”

A moment later, referencing his own feelings in the symphony’s aftermath, Glass casually declares that “Writing it and hearing it is not exactly the same.” In a nutshell, this dichotomy is at the center of our discussion: how, for a composer, especially one as long-established as Glass, the acts of conceiving and listening are both intertwined and separate, and how such actions relate to one another when writing a massive piece such as the Eleventh.

For Glass, some notions of these concepts arrived early. Though he began attending Baltimore’s prestigious Peabody music school at the age of eight, he’s certain that “My days of listening were connected to my father’s record store, where I began working when I was 12. My first job in the music world was advising people what records they should buy, so I had to know all the records in the store. They would come in and say, ‘Well, I want to buy Beethoven’s Third Symphony’ and I would say, ‘Do you like it fast or do you like it slow? If you like it slow, you can get Bruno Walter’s. If you like it fast, we can get you Toscanini. If you want an American version, we got Leonard Bernstein’s.’ I had to listen professionally, you might say.”

Glass’s listening also needed to be mindful of the budding audiophile market. “We were aware of which were the good sounding records and which were not, but the people who were nuts about sound they didn’t care about the content. We’d say, ‘We just got a new marching-band record, you won’t believe how the brass sounds.’ We were selling music.”

As Glass moved through his schooling and creative evolution — at the University of Chicago and at New York’s Julliard School of Music; then in Paris, studying with the famous composition teacher Nadia Boulanger and notating the Indian music of Ravi Shankar; then back to New York, where in 1967 he founded the Philip Glass Ensemble for the performance of his own budding compositions — he says, “I hardly listened at all.”

Glass’ fluency reading music and imagining it off the page accelerated his understanding of compositions and its forms. “I would pretend to be following lectures and actually I was reading a Beethoven quartet,” he says of racing the pedagogues and winning “because I could read faster.” Yet he also recognized the flaws in conceptualizing composed sound without actually listening back to it. “Are we hearing it accurately? Are we writing down what we want to hear?” Glass asks. In his mind, the greatest challenge of imagined accuracy is “hearing the music in real-time. It’s very hard to do. So you end up playing it on the piano,” which, if the piece is symphonic, is not the music’s true representation either. The relationship between linear time and writing is a life-long conundrum. “I think these are challenges for composers at any point in their life. You don’t get particularly better — you may learn certain tricks, but that’s it.”

Technology has certainly changed his landscape. It is interesting to hear Glass — who recently had a Sonos system set up throughout his house — discuss digital tools as “assets” in his process. Including, in the writing of the new symphony.

“I was working with Dennis,” he recounts of the lead-up to the Carnegie Hall premiere. “We were going over some transitions, and he had the rehearsals on a digital recorder. I had it put on Dropbox, pulled up the rehearsal on my phone, so we listened to it together, and would say, ‘well maybe we can cut a couple of measures here.’ Now in my music room, I tend to listen to playback of things, the rehearsal tapes. That became very useful.”

Aging has done its share to affect how Glass’ hears — “Perceptual faculties become degraded biologically,” he says, matter of factly. “Look I’m 80, what else is going to happen?” – but also, more importantly, what he chooses to hear.

“Mostly, I listen occupationally. Of course it’s fun to listen, but I don’t listen for fun. When I listen to Anoushka Shankar’s new album, for instance, I am more listening to see if she’s got a good band, if they’re playing together, would Ravi be happy when he heard it. Or, if I hear an orchestra, I want to hear the conductor, I want to hear how they sound.” The smirk rises to the fore once more. “I have all kinds of sinister agendas for listening tucked away.”

Glass says that, beyond music, he has other reasons to love his Sonos set-up. “I find that in my bedroom, I listen to the news — the stations are listed and they don’t drift. But listening for pleasure…” His voice trails away. “My ideal place is some place where they don’t play music. I found for example, that Chinese restaurants in New York don’t have music, have you noticed that?”