Last month I finished recording an audio version of my new book in four days — a full day ahead of schedule — and I was feeling pretty good about it. It helped that the audio technician at ­DuArt, a film and recording studio in Midtown Manhattan, could hear like a bat and caught every stomach gurgle. As I was about to leave, I jokingly asked the audiobook studio director if he could make the book a runaway audio best seller.

“You should have written a smut novel,” he told me. “Those are the ones that sell.”

“Who in the world listens to smut novels?” I asked.

“Long-haul truck drivers!” he replied.

He was pulling my leg, but only slightly. Audio recordings of erotic fiction are a booming business. Long-haul truck drivers — who buy audiobook CDs at travel centers on the road — are just some of the enthusiastic listeners. The explosion of sex-infused books (much of it self-published) and the popularity of MP3 downloads have combined to produce a vast universe of fictional aural sex. The books range from fantasy romance with rose petals on the bed to raunchier fare with lots of rough sex.

“Listening to an audiobook can be done anonymously, in the car, on the subway, at the gym,” said Troy Juliar, the senior vice president and publisher of Recorded Books Inc., the largest independent audiobook publishing company in America and Britain. “Sometimes listeners get hooked on a series — or seduced by a voice — and want to hear more and more. The voice in romance and erotica is more intimate, so it’s doubly important.”