The bluegrass group Time For Three, famed locally since its impromptu session at the Mann Center for the Performing Arts when the power failed during a concert four years ago, has traveled the country to enormous success. The trio of bassist Ranaan Meyer and violinists Nicolas Kendall and Zachary DePue asked Higdon for a piece - then found their friend had written them something seriously difficult.
"All three played in the premiere of 'blue cathedral,' " said Higdon of the classically trained musicians. "I knew Zach from when he was 5 or 6, and when I studied composition with his father, Wallace DePue, at Bowling Green University, he was always running through the building.
"There are three movements in 'Concerto 4-3,' and the last two begin with them playing before the orchestra enters, so they could improvise transitions in between. I said, 'Are you sure you guys want to go up there and improvise something different every night?' and they said yes!"
Higdon had written a sonata for Koh, who then asked for a piece using violin and chorus.
"David Hayes [of the Philadelphia Singers] thought it should have a chamber orchestra, and in discussions with the Philadelphia Orchestra's Kathleen van Bergen, 'The Singing Rooms' became a concerto.
" I needed texts that would support a 30-minute structure, so I chose works by Jeanne Minahan McGinn, who teaches English and liberal arts at Curtis, and made a conscious choice not to write a really difficult choral part so community choruses could do it."
The two concertos weren't intended to be performed in tandem; it just worked out that way.
You'd think Higdon would be elated right now, but these weeks and days before the concerts are difficult.
"This is the most terrifying part of being a composer," she explained. "Sheer terror, being on top of both scores in my head. There's only one rehearsal for each work before the final dress rehearsal, so I basically have one chance to change anything on the spot. If it isn't just right, I have to decide if it's a problem with what I've written in the textures or whether they simply need to learn the music more.
"And soloists, plus a chorus, add more dimensions, so with the Jenny Koh piece, I have to guess what a problem might be and fix it right at that moment. I'll continue to adjust it, because it's already scheduled for Atlanta [where it will be recorded for Telarc] next year, and then Minnesota, and [conductor] Marin Alsop just asked when she can have it."
Higdon publishes her own music, and it's so in demand that her partner, Cheryl Lawson, works six days a week filling orders, mailing scores and dealing with requests to their Lawdon Press.
Every week, there are about five performances of Higdon's music somewhere - so many that she can't go to them all.
Higdon is home in Philly for a rare six straight weeks during this busy period. Besides the orchestra performances, Network for New Music is playing her "Bentley Roses" on Wednesday, and there's an upcoming performance of an English horn piece for the orchestra's principal Elizabeth Starr Masoudnia.
And that's not all.
There's a Violin Concerto for Hilary Hahn and a Piano Concerto for Lang Lang, who had it for eight months and asked for 30 bars of revisions. Then, in a surprising development, he sent Higdon a message saying he just couldn't do it.
"I asked Gary Graffman and Hugh Sung at Curtis if it was playable, and they both said yes. Hugh even said he would do the fingering and even play it, which I would have loved, though the National Symphony [which commissioned it] wanted a big name for publicity reasons. I really don't know Lang's reason [for declining], but Yuja Wang will premiere it with the National in 2009."
Creation is a mysterious enterprise, with hours of solitary soul-searching. Higdon, just 45, still feels a little bemused by her enormous success.
"It's very surreal," said Higdon, "because I grew up around artists in different stages of difficulty and know it's not a kind world for artists. I work every day, especially in the mornings, and it's still elusive and scary. I often say I can't remember how to write, and give myself permission to throw stuff away.
"I always think that the inspiration is not me, it's coming from somewhere else. I'm often startled and say, 'Where did that come from?'
"It helps to be ready . . . knowing practical stuff like the instruments and how sounds combine. But when ideas come from some big place in the sky, it's good that you're sitting there with your hands poised, aware enough to pick up on signals."
As for the two premieres awaiting Philadelphia concertgoers, "I'm excited," their creator said. "I absolutely guarantee the audience will like them!" *
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"Concerto 4-3," 8 tonight, tomorrow and Tuesday, "The Singing Rooms," 8 p.m. Jan. 17-19, both works, 8 p.m. Jan. 23, and 2 p.m. Jan. 25, Verizon Hall at the Kimmel Center, Broad and Spruce streets, $10-$113, 215-893-1999, www.philorch.org.