It is not often one has the opportunity to meet the beast in its lair, and so when the chance came to visit Muzak in its headquarters here, it was, of course, accepted. O, sound most banal; O, unholy technological choir; O, the burgeoning urban squall! Not that a good reporter is ever subjective.

Politesse was the order of the day when arriving at the company's silver and modern offices, and being introduced to Ron Baum, the director of programming.

"Your music incites me to rage," said the reporter.

"Aaaah," he said, as sweetly as the version of "Younger Than Springtime" wafting down the halls. "A Purist. I used to be like that myself before I came to work here."

He's 42, a former disc jockey but in his current incarnation responsible for the listening diet of some 80 million Americans, perhaps the most powerful disc jockey in the world. The sounds of the supermarket, Muzak over the elevators, music in the jetliners before takeoff -- all that is his doing. And if those tunes sound to you very much like one another, if often you realized that you have not even realized that the Muzak is there, well, that is all to the good. The point of Muzak is not entertianment, but environment.

"A highly technical procedure designed to create a predetermined response among listeners," Baum likes to say. For this he has a top-flight technical team: Computers, which check every tune before airtime to make sure, it's flawless. ("The computer has a great ear," an executive says.) A satellite, to beam Muzak all over the world. (Argentina leads the subscribers.) And of course, the time-honored Muzak system of "stimulus progression," their famous method of "reducing stress, boredom and fatigue while increasing productivity."

"We play music scientifically," says Baum, in his lovely, mellifluous voice, "in a pattern of 15-minute segments, with individual tunes placed in order of ascending stimulus value. That's actually 14 minutes of music, with a one-minute break; but it's actually so accurate you could set your watch to it -- if you're in an elevator and the Muzak comes on, you know it's the top of the quarter hour. The stimulus group is programmed in an ascending pattern throughout the morning, then lower toward lunch hour, when you're winding down, then ascending again reaching a peak at 3 in the afternoon -- it's always a question of playing against the down time. . . .

"We also create speical programs. We supply boarding music . . . . in that case we'd want bright, cheerful, music; we'd want to avoid playing anything that might have adverse connotations -- let's say a hit that dealt with a plane crash, not that I can think of a song about a plane crash. . . ."

He has no doubts that Muzak, in its 46-year history, has worked well. He points to studies that prove Muzak has increased worker prodictivity. He tells happily of a plant where workers decided they wanted their own music, not Muzak, and after a month of continuously turning the radio dial, switched back to Muzak. ("That's the essential thing about Muzak," he says, "it appeals to 90 percent of the people. Though not the purists, of course.")

He adds that Muzak records only its own arrangements; that the preferred music directors are people "who are good at TV background music or commercials . . . 'sell' music." He says that while "Raindrops Keep Falling on My Head," is a fine Muzak tune -- as are many Burt Bacharach songs -- it is not the most often-played Muzak tune. Excessive repetition has an adverse effect on people, so Muzak, mindful of their system, doesn't play anything too often.

Which is not to say they don't make mistakes.

"A few years ago Judy Collins had a big hit with 'Amazing Grace' and we, of course, recorded it," says Baum cheerfully. "We didn't know that 'Amazing Grace' continues to be used at funerals in the South -- the minute those tapes hit North Carolina, we had problems. Then we had another hit -- 'El Silencio' -- the first two measures of which sound like 'Taps'. We played it the day after President Carter had a minor jogging accident, and the phones went wild, people calling up saying, 'My God, is the president dead?'"

He smiles. "That was the end of 'El Silencio'."

End of story.