NEW YORK – “When stuff is coming to an end, people freak out and they act crazy,” says Liz Lemon.

Liz and all the characters of “30 Rock” are doing just that on the series finale (airing Thursday at 8 p.m. on NBC) as they produce one last installment of their show-within-that-show, “TGS,” while anticipating life apart from one another.

But Jeff Richmond wasn’t freaking out, not even with the end (and a tight deadline) breathing down his neck: Just last Friday he was in a studio in midtown Manhattan, closeted with an eight-piece string ensemble, his baton raised, recording interludes of background music for that final episode.

After seven seasons (plus 14 Emmys, six Golden Globes and a Peabody Award), there are many reasons to remember “30 Rock” fondly:

The silky self-importance of soon-to-be-former Kabletown CEO Jack Donaghy (played by Alec Baldwin). The naked, comically off-kilter ambition of “TGS” star Jenna Moroney (played by Jane Krakowski). The manic abandon of her co-star, Tracy Jordan (played by Tracy Morgan).

There’s Kenneth, the toothy true believer (played by Jack McBrayer), who last week was promoted from janitor to president of NBC.

And could any viewer ever forget the unexpected newlywed and mother of adopted twins played by “30 Rock” mastermind Tina Fey? As the frazzled, none-too-spunky producer of “TGS,” Liz Lemon has been a new-millennium Mary Richards for whom “you’re gonna make it after all” always seemed a long shot.

But Jeff Richmond – an unseen, unsung hero of “30 Rock” – has been essential, too, for his service as the composer and arranger of the show’s distinctive score (in addition to his duties as executive producer and, by the way, Fey’s husband of 12 years).

At the show’s inception, Richmond composed the “30 Rock” theme song, which, in its tight 17 seconds, teems with cultural references and preparation for the show it introduces.

“It’s got a Gene Krupa drum thing and a baritone saxophone, like you’d hear in a burlesque show,” he says, listing some of its influences, “and it’s very New York – Cy Coleman, Frank Loesser. And the doo-wop singers make it feel a little retro.”

For fans of “30 Rock,” that theme by now seems second-nature.

But every week since the show debuted in fall 2006, Richmond has fashioned the background music that sonically frames the madcap action.

“The writers do such a great job creating these intricate stories,” he said. “The music helps clue the audience in to the recurring patterns and themes.”

Thus is the music Richmond conjures a guide and an organizing principle. It is treasure buried just beneath the surface of the viewer’s consciousness, enhancing the personality of “30 Rock” – without the audience even needing to notice.

On Friday, Richmond was presiding at a major scoring session for the hour-long finale at John Kilgore Sound & Recording.

“I’m tired of writing goodbye music for all the characters,” Richmond said with a laugh.

For instance: The show’s “Liz” theme – a bouncy, familiar tune heard since the very first episode that was often arranged with a Scott Joplin lilt, but here was reimagined as lush and sentimental.

With Richmond busy in the studio, Kilgore was in the control room piloting software that resembled a souped-up version of GarageBand while “30 Rock” music producer Giancarlo Vulcano logged the progress on a laptop and old-fashioned sheet music.

Next to be recorded was a piece that sounded like a mash-up of Aaron Copland and Leonard Bernstein; “Hoedown” meets “On the Town.”

“Jeff, I like that take,” said Vulcano at one point. “But it should be, almost, ethereal, yeah?”

“This is Jack’s big happy montage,” agreed Richmond. “He’s finally happy. He’s finally killing it!” Richmond addressed his musicians: “You ever see that movie ‘The Natural’? Like, when Robert Redford hits that ball up in the air?”

Everyone laughed.

A large recording session isn’t the norm for “30 Rock.” More often, Richmond layers the instruments one on another, with many of them played by him.

“It’s not because I’m a great player, it’s out of necessity: I work so late, I generally can’t write charts for seven or eight pieces of music and bring players in,” he explained. “I play the piano and saxophones and clarinets. Giancarlo is very gifted with the guitar, banjo and ukulele.” Strings and percussion are usually synthesized, “but every triangle you hear is real.”

Now the end of “30 Rock” was approaching. What’s next for him? Maybe a collaboration with Fey on a Broadway musical version of her 2004 film “Mean Girls,” he said. Maybe scoring a movie. “I’m open for anything.”

As the minutes ticked by last Friday afternoon, Richmond wasn’t freaking out.

“It’s all lining up nicely,” he said, exuding confidence as he cued the strings for another take. “But I’m still not finished writing. I’m still figuring out the last piece of music you’ll ever hear in the series. I’ll record it over the weekend.”