CHICAGO • A few years ago, after they had shared more than a couple of post-concert martinis, cellist Yo-Yo Ma made a request of composer and conductor Esa-Pekka Salonen: Write me a concerto.

That is the kind of offer you cannot refuse and the two happily, tipsily shook on it. The only problem? The commitments of the night before seemed, as they can in the haze of a hangover, a little sketchy the next morning.

"I knew with absolute certainty that we had agreed on something," Salonen dryly recalled a few days ago. "But I wasn't sure on what."

When his memory was eventually jogged, plans were set in motion.

Last week, Ma, 61, Salonen, 58, and the Chicago Symphony Orchestra presented the concerto's premiere in Chicago.

Racing across the country, Ma on Wednesday will play the fiendishly difficult piece - in which the cello does battle with a swirling orchestra, a hyperactive set of bongos and even, through live tape looping, its own shadow - with the New York Philharmonic under Alan Gilbert.

What was the experience of working on this?

Ma: With a piece of new music, I go through a phase where I ask myself: "Why was Esa-Pekka angry at me? What does he have against the cello? Why are you torturing me with impossible things?"

I go through that and finally get to: "Oh, this is very interesting. Okay, uh-huh, so this is how that works." And I gradually get more and more into it. I can't tell you how many versions I go through, translating the score into physical engineering. With this, I was worried about the music coming through, and projection.

Salonen: That was the first thing he said to me when we went through the sketches: "So, should I be amplified or not?" And I said, "I'll try to be careful." The thing about the violin is you can always soar; you can go above the orchestra. But the centre of the cello register is where it's generally densest in the orchestra.

And, if you want to create any kind of sonority or resonance within the orchestra, the notes that you usually use for that are taken by the cello.

So you have to be very careful because if you pack too much stuff in the same range, it just disappears.

So did you find ways to tailor it to your knowledge of Yo-Yo?

Salonen: What fascinates me about performing, especially when I see Yo-Yo perform, is the communication. The fact that whatever he does is meant to come out and reach out. And I thought I could build on that quality in the finale. The gestures become amplified and that sort of communication becomes like hypercommunication.

Ma: He said, "At the end, you should feel burned up."

Salonen: It's like a heroic end.

Many people at intermission were talking about the looping in the second movement: haunting echoes of cello fragments that seem to travel through the hall. What are you trying to convey?

Salonen: I had this idea of music that would seem like it was being born at that very moment, that it wasn't "composed" so much.

And I thought with looping, there's a random element to it. You can control it, obviously, in terms of what is being looped, but you can't control it in terms of how it comes out, precisely because of the randomness of the layering.

Ma: It's not, "Oh, we're using that technique". It's enhancing the aesthetic you had naturally; it's very organic. Just like in the piece, you're doing something different than direct quoting or paraphrasing of Lutoslawski or Tchaikovsky, but you pick up lots of influences. Just whiffs. They're the DNA building blocks.

And if someone else studies this work, he will find things in it that he can build on top of, and that's what makes things grow.

Salonen: I think that the very beauty of this thing we call classical music is that you build on your predecessors' work and you become part of this fabric which we call history.

NYTIMES