There's no sign on the dark glass doors of the Books on Tape recording studio tucked into a plain-wrap business park in the Woodland Hills section of town, nothing to indicate that life's certainties -- death and taxes, as well as sex, heartbreak, war, murder and religion -- are regularly talked about within.

The state-of-the-art studio, built in 2004, handles the production of 400 audiobooks a year. While the music and publishing industries struggled in the last few years, audiobooks enjoy annual growth spurts of 15 percent a year. They constitute an $800 million-a-year market, according to the Audio Publishers Association, and the proliferation of Web sites offering digital downloads is making audiobooks more affordable and convenient for America's 42 million owners of iPods and similar devices. AudioFile magazine, which reviewed 2,100 books in 2005, estimates that 2,500 to 3,000 titles are recorded each year for sale to libraries and the public.

On a typical recent weekday, all six of the facility's studios were in use. At midday, a stellar group of narrators, all in the process of recording novels, gathered in the lunchroom. Although a majority of the 40 to 50 in-demand readers in Southern California also act in television and film, the best and busiest could make a living just recording audiobooks.

Paul Michael, whose voice is familiar to anyone who listened to "The Da Vinci Code," had spent the morning recording the latest Dean Koontz novel. Scott Brick, whose personal best is recording 200 books in a single year, was narrating a thriller, "The Skin Gods," by Richard Montanari. Kathe Mazur, who followed Hillary Rodham Clinton's "Living History" with Ann Coulter's "Treason," was in the midst of "Veronica," a novel by National Book Award finalist Mary Gaitskill. Kirby Heyborne was finding his voice again after a morning of speaking as a 13-year-old British boy, the narrator of "Black Swan Green" by Booker Prize finalist David Mitchell.

"At the end of a day like today," Heyborne said, "I get home and I can't talk, or read, or watch TV, or anything. I'm just completely exhausted."

The others understand. They know the challenge of voicing a dozen characters in a scene heavy with dialogue, how the rustle of a starched shirt or a gurgling stomach can ruin a perfectly executed paragraph. They have learned how to sound the same at the end of the day as at the beginning and have mastered the pronunciation of arcane words that most people simply read past. Alone in a chilly, darkened studio with only a director and without feedback from an audience, they carry the narrative, even for books they don't like.

After lunch, Brick heads back to a small studio, where a glass window separates him and his director, armed with a bottle of water, breath mint drops (to foil cotton mouth), a thermos of throat-coating tea and Blistex, a hedge against the dreaded sound of dry lips smacking together. Water, mints, tea, Blistex. Whenever he pauses to turn a page, he uses each item, in turn. He reads with remarkable fluidity, flubbing only once in five minutes. Water, mints, tea, Blistex.

If modern existence were simple, there would be no need for magazines that teach the harried how to streamline their lives. Increasing traffic adds extra minutes, even hours, to commuting, making a 24-hour day too short. Reading is more readily given up than sleeping or eating, but not by those for whom time on the road isn't wasted. More than 50 percent of audiobook listening is done in cars, and listeners who aren't vehicle-bound are otherwise multitasking -- they exercise, garden or do chores wearing earphones.

A survey done by the trade association found the average listener earns 25 percent more than nonlisteners, has a higher level of education and is more likely to hold a professional or managerial position. "We've always reached the hardcover buyer more than the paperback buyer," says Chris Lynch, publisher of Simon & Schuster Audio.

Most people born after World War II didn't grow up with the mysteries, thrillers, adventure yarns and romances that flourished during the golden age of radio, so they aren't accustomed to listening to stories read aloud. Yet they acquire the skill quickly. "Audiobooks are very much a try-it, you'll-like-it thing," says Shannon Maughan, audio editor of Publishers Weekly. "I don't know many people who've turned back, once they've tried it."

With iTunes, Audible.com, Mediabay.com, Jiggerbug.com and other Web sites sending downloadable audiobooks through cyberspace, prices will inevitably go down. "The distribution and delivery system of downloadables eliminates a lot of different kinds of overhead," says Maughan of Publishers Weekly. "You're not shipping, warehousing and producing expensive packaging for every book."