From the college lecture hall to your headphones

She calls it a "dim sum PhD."

In the past five years, Lucinda Robb has absorbed roughly 400 hours of academic lectures at 60 universities. She's always on the hunt for that perfect blend of solid knowledge and electrifying delivery.

And for all this learning, Ms. Robb earns a paycheck. She's a recruiter for The Teaching Company, which has been delivering audio and video courses to the self-taught set for more than a decade.

Whether they're commuting to work or hammering out miles on the treadmill, people have made these digital professors part of the fabric of their lives.

The lectures "have turned the Long Island Expressway into an opportunity instead of a nightmare," says Richard Kossman, a neurologist in New Jersey who listens while commuting in his champagne-colored BMW.

Tom Rollins, CEO and founder of The Teaching Company, says there are three specific qualities that separate certain teachers into a class of their own: depth of knowledge about a subject, extraordinary communication skills, and passion.

"Great teachers think they have figured out something about the universe that they think no one should go through life without knowing about," Mr. Rollins says. "They love the subject and they want to share that passion with other people."

The company has chosen more than 100 professors who fit the bill. Their collective recordings top 2,000 hours.

Robb compares her job to that of a football recruiter - but instead of scouting talent from the sidelines, she's at the back of the classroom. Recommendations for new recruits come from a variety of sources - editors on the student newspaper, course evaluations, teaching awards, and sometimes the professors themselves. The company's goal, in part, is to pick lecturers who remind people of their favorite college professor, the one who showed such enthusiasm for a subject that the classroom wasn't just a location, it was an experience.

But recruiting is not without its challenges, such as trying to find more women to record lectures. "So many women profs don't lecture. They are much more likely to offer seminars and engage with their students through dialogue," Robb says.

Once a professor clears the audition hurdles, a grueling process lies ahead. First, a professor submits his or her courses for review. They must be tailored for a 30-minute recording with no tangents, no forgetful "ums," and no stopping for questions. Then comes the recording session in a studio near Washington, D.C.

At that point, a lecturer must "come loaded for bear," says Robert Greenberg, the music historian in residence at the San Francisco Conservatory. He's been working with The Teaching Company from its inception and has recorded 246 hours of lectures on musical masters and their works.

In the studio, the lecture script rolls on a teleprompter. As the professor delivers his or her talk, a live audience laughs when appropriate and claps politely. The age of digital recording has allowed professors to correct gaffes, but mostly the lectures are done in one shot.

Finally, recordings are sent out for a sample of customers to preview, and their feedback determines whether a professor makes the cut.

The whole process - from recruiting to a finished product - can take eight months.

Once they have a relationship with The Teaching Company, professors constantly work on new courses to offer customers.

Audio and video learners aren't just retirees with time on their hands. They are multitasking baby boomers who drive to work wanting to know if Hitler could have been stopped if the world had acted sooner. They are doctors and accountants who want to stretch themselves to relearn the Greek classics. And they are families at the dinner table, listening together in a tradition that has made the professors, well, part of the family.

Professor Greenberg receives 30 to 50 letters and e-mails a month. Many write to say there's an open spot at their table if he's ever in town. He rarely takes them up on their offers.

"I think there's a tremendous hunger out there for information well transferred," Greenberg says, "where the information isn't dumbed down, where stories [about historic figures] aren't told as if they are dead or deified. We still have to think about people like Mozart as a human being, so we can understand him as a person and get inside his music. I don't want to apply a veneer of godhead to put an even greater historic distance between us and [people of genius]."

It's this kind of approach that keeps customers coming back for more. After all, who doesn't like to trot out these kind of tidbits at dinner parties: Did you know that the ancient Greeks were convinced that thought originated in the midriff? Or that early experiments with electricity involved the limbs of frogs dangling from a wire during storms?

For Lois Rentsch, watching video lectures is part of the daily drill. Ms. Rentsch taught public school for 41 years. Now retired, she tutors and teaches Greek to a group of priests at her church. In her home office, Ms. Rentsch becomes a student once again. Even though her personal videotape library consists of 297 lectures, she does have limits: "Not more than a couple of hours a day, max," she says.

But Rentsch is not without criticism, "I've got to write to one professor and ask him about his hideous sweater," Rentsch says. "His wife must have knit it for him."

It goes without saying, professors can always learn a thing or two from their students.