Mario Piraino tells the story about the factory worker who called home and said he had to work late that night. "The wife is suspicious, see, but she can hear in the background the sound of the factory, the clanging and the crunching, so she believes "

Mario suppresses a smile. "The truth of the matter is, the guy's got a tape cassette with him in a phone booth at a bar and he's playing factory sounds on the tape "

Marlo laughs loudly at that, then shakes his head. "We got tapes for everything. Office sounds wit, typewriters, a stomach growling, even a baby falling down the stairs."

He makes a grand gesture with one arm. "You name it."

Mario Piraino, who is not too tall and talks very fast, is a sound junkie.

He and his wife, Mignon, the Mistress of Magic some years ago when she was playing places such as Larry Potter's Supper Club in Los Angeles and the Clover Club in Portland, Ore. ("A Show to Fit Any Budget "), run a shop called Knight Educational Recordings in Los Angeles.

They have been there for 30 years and Mario, who is his own best salesman, will tell you flat out that he started the whole educational industry on record and tape.

Later he will qualify that somewhat, saying he was one of the pioneers in the industry, because God knows who was doing what when. "You can't tell," Mario says generously.

Whatever the case, he has built sound into a thriving business.

The Pirainos offer 17,000 different titles for sale on records and cassettes, about 1,000 of which they produced themselves. They distribute the others for various companies.

One can purchase an infinite variety of sound effects and educational recordings from Mario and Mignon. Not just the baby falling downstairs, but the sounds of a junkyard, crickets chirping, meat grinders grinding and, for those who miss war, the cacophony of combat.

"Are you ready for this?" Mario leans over the counter. "Let's say you're a widow living alone. It's two o'clock in the morning. Suddenly, you hear someone outside a window."

Mario pauses for effect, letting that sink in. "You come downstairs quietly" -- his voice lowers -- "and you slip a tape into your cassette."

Now he shouts: "Dogs barking and growling and howling and away goes the burglar He thinks you got an army of killer dogs there " Mario nods with satisfaction. "You're safe."

But not everyone, Mario realizes, needs barking-dog sound effects or mating whales or foghorns or North American frogs croaking.

How about a nice biofeedback cassette intended to alleviate male impotence? Mario winks and puts on a tape.

Out comes a sexy female voice telling you to relax, fella, to let every part of your body loosen and to think of, well, her and her body.

"We had a customer who fell in love with her voice," Mario says, turning off the cassette and shaking his head.

"Down, boy," Mignon warns.

"We've got it all," Mario continues, walking through his sound shop and pointing out this and that, "Old-time shows, poetry readings, Bible stories, how to invest, the principles of flower arranging, talking cookbooks . . .."

Mario's tapes and records, he says says firmly, can teach your baby to talk, help you overcome depression, enhance your metaphysical powers, teach you Swahili, and train your parrot.

There is also a record called Co-Star that comes complete with a script for those who have always wanted to be in a play.

"What do you," Mario says, "is put on the record and turn on a tape recorder too. There are blank places in the record where you do the play. Terrific?"

Mario traces his interest in sound back to high school where, he will admit, he was not a terrific student.

"The teachers talked too fast," he said, talking fast, "and when they'd say something and you didn't get it you couldn't ask them to say it again because they'd get made. You understand?

"So I taped a lecture one day, using the old wire recorders they had then and it worked great I've been doing it ever since."

Business has been good for Mario and Mignon.

He is disinclined to talk about money except to say that business is up 30 percent so far this year over last.

"We have increased every year since we sat in a little room and sold our first 10 records," he says. "It's a tense world," he adds, shaking his head. "There's no time, you know? So you slip a cassette into your tape deck and learn Arabic as you drive to work."