Saturday night, 8 p.m., bustling downtown Bethesda. My partner and I, self-appointed members of the noise police, are patrolling the bar at the hot new French bistro, Mon Ami Gabi.

"What did you say?"I ask.

"I said it's averaging 85 decibels in here," she shouts, pointing at the small, rectangular machine she's holding in her hand. It's a sound level meter and noise-logging dosimeter, the kind of heat audiologists pack when they head to a crime scene.

Hey, she's not your typical partner. She's Sandra Gordon-Salant, a hearing and speech professor at the University of Maryland and an expert on noise, speech perception and aging. Me? I graduated from the school of hard knocks, having gone deaf in one ear nearly two years ago. (If you have to know, I majored in Humility & Hearing Aids.)

We're both baby boomers who have hired babysitters to spend a night on the town. Our mission: to find out if popular local restaurants -- we picked five in Bethesda -- are really impossibly noisy or if we're just getting old, cranky and oblivious to a good time.

You be the judge. My job? Get home by 11. Whoops, let me try that again. My job? Just the facts.

Fact #1: If you've read this far, you're probably old enough to have age-related hearing problems, restaurants or no restaurants. Sit down for this revelation: The older you are, the more likely you are to have trouble hearing. In a recently published analysis of a 1998 survey conducted by the Centers for Disease Control and Prevention (CDC), a mere 5 percent of people aged 18 to 44 report "a little" or "a lot of trouble hearing." No surprise, the numbers go way up for those between 45 and 64, with 14 percent of women and 27 percent of men acknowledging the problem. For those over 65, get out the megaphone: 35 percent of women and 50 percent of men report difficulty hearing.

That's bittersweet news. On the one hand, chances are high that you'll have trouble hearing as you get older, particularly if you're male. On the other hand, millions of women can now entertain the notion that their husbands are not actually ignoring them, but rather can't hear what they're saying.

Fact #2: One of the first signs of hearing loss is cupping your ear and saying, "Huh?" a lot in restaurants.

Don't believe me? Go to the American Speech-Language-Hearing Association's web site (www.asha.org) and take the 14-question self-test designed to determine if you've got a hearing problem. Question #7: "Do you have trouble hearing in restaurants?" #6: "Do you have trouble hearing in a noisy environment?" And #9: "Do you find yourself asking people to repeat themselves?" More than two affirmative answers and in the Game of Life you've picked the card reading, "Go to audiologist. Miss next turn."

Gordon-Salant explained it a bit more scientifically. "In the case of a restaurant," she said, "the background noise is composed of people talking -- speech -- which has the same frequency composition as the target signal, speech." The background noise "directly masks" what you're trying to hear. In other words, you're left trying to distinguish subtle details in a complex white-on-white design.

When you begin to have more trouble doing that than you used to, wake up and smell the coffee. Your meal is coming to an end.

Fact #3: Loudness, like most things in life, is all a matter of degree.

Rustling leaves register about 20 decibels, a quiet library or a whisper registers about 30 decibels, normal speech 60 to 65, a vacuum cleaner or city traffic 80, a lawnmower 90 to 100, a rock concert 120, a jackhammer 130 and an air raid siren 140.

It's also important to know that perceived loudness doubles with each 10-decibel increment. That means 80 decibels sounds about twice as loud as 70. And that 140-decibel reading can really hurt.

Fact #4: Every decibel matters, particularly in noisy environments.

To explain, audiologists refer to the "signal-to-noise ratio," a measure of the sound you're trying to hear vs. the background noise you're trying to ignore. For optimum comprehension, Gordon-Salant said, you want the dinner conversation to be 30 decibels louder than the background noise. So if normal conversation registers 65 decibels, you want the background noise no louder than 35.

When the background noise is louder, you hear less. For instance, if your speech measures 65 decibels and the noise level is 65 decibels, you understand only about 50 percent of what's said, experts say. If the noise level goes up by just one decibel to 66, your comprehension drops to 40 to 45 percent. To compensate, you've got to talk louder and move closer to try to understand what's being said.

Fact #5: Most restaurants are really loud.

A few years ago, the San Francisco Chronicle responded to reader complaints about loud restaurants by adding noise ratings to its reviews. Working with Robert Sweetow, director of audiology at the University of California, San Francisco, and author of the article "I'll Have a Side Order of Earplugs, Please," Chronicle reviewers devised a noise rating system using four bells (deci-bells, get it?) and a bomb.

Noise under 65 decibels rates one bell for "pleasantly quiet." If the noise goes up to 65 to 70 decibels, restaurants get two bells, but you can still "talk easily." Three bells (70-75) means "talking normally gets difficult." Four bells (75-80) means you "can only talk in raised voices." And reviewers drop "the bomb" when noise tops 80 decibels and it's "too noisy for normal conversation."

Most restaurants reviewed by the Chronicle score between 73 and 78 decibels, rating three or four bells. And that's what we found in Bethesda.

It's important to note that our mission was hardly undercover. We stopped in five Bethesda Row restaurants, pulled out our dosimeter and asked to see the manager. After securing permission to measure sound (not one manager objected), we cased each joint, collecting kitchen-counter intelligence and gauging the average noise level in each. Our camouflage gear (we both wore black) and low-key mannerisms worked, as patrons paid us no mind.

Using the Chronicle's system, we concluded that none of the five restaurants we visited is ideal for meaningful conversation, at least not on Saturday night. Delhi Dhabi, an Indian restaurant, was the best of the lot, rating a mere three bells, perhaps because of the acoustical ceiling tile, carpeting and tablecloths, or possibly because it was only two-thirds full.

Austin Grill, Tara Thai and Jaleo were packed and racked up four bells each. The noise actually could have been worse, but each has made a few concessions to their concession. Austin Grill separates its small bar from the dining room with a partial wall, and the lowered ceiling with the giant prehistoric lizard likely absorbs some sound.

Tara Thai packs its tables very closely together, which can be very tough on conversation (and privacy), but has acoustical ceiling tiles, upholstered benches on one wall and no music playing. Jaleo's flashy design includes a lot of contours, upholstered benches and acoustical ceiling tiles to absorb noise that bounces off the wood floors and huge windows.

Now, don't think I'm patriotically picking on the French, but the worst rating went to Mon Ami Gabi. Using the Chronicle scale, the bistro got the "bomb." I can only describe the noise as a thunderous rumble, forcing those at the bar to shout in each other's ears just to be heard. High ceilings, tile floors and hard walls didn't do much to help. When you're paying $26 for a New York strip, it seems to me you have a right to expect conversation with that. Not here.

Fact #6: Loud restaurants can be especially tough on people with hearing loss, for more than the obvious reasons.

First, those with typical age-related hearing loss are often, consciously or not, counting on contextual cues and lip reading to make up for what they don't hear. In a loud restaurant, that's harder to do, not because they can't read lips in restaurant lighting, but because it's tough to fill in the gaps of the conversation when they've heard so much less of it to begin with.

Second, counterintuitive as it seems, many people with trouble hearing, particularly those who have nerve damage (that's me), have a reduced tolerance for loud noise. You might think that people who can't hear well wouldn't notice if the volume were jacked up or might even appreciate it. And that may be true -- up to a point.

Unfortunately, Gordon-Salant explained, "The range between detection of noise and an uncomfortably loud signal is compressed in many hearing-impaired people. Normal-hearing people don't start to experience tolerance problems for loud sounds until the signal is 120 decibels, but hearing-impaired people may experience reduced tolerance at about 100 decibels or lower." Guess I'll pass on the live music, thanks.

Third, not all hearing aids have directional microphones that attempt to pick up only the conversation you're trying to hear. The rest, mine included, pick up all the background noise; some even amplify it.

Fact #7: Most restaurant noise is not dangerous to your health. Just annoying.

Despite his request for "a side order of earplugs," Sweetow said, typical restaurant "noise levels are not hazardous to restaurant patrons." Gordon-Salant agreed, adding, "The most detrimental effect of elevated noise levels in restaurants is the reduced ability to understand a conversation."

Most experts agree that permanent noise-induced hearing loss only occurs if you're exposed to a one-time blast that's off the charts (think bombs, not breaking dishes) or noise levels over 90 decibels for eight hours a day, over the course of five to 10 years. (Think musicians in persistent rock bands, not Muzak in The Cheesecake Factory.)

Fact #8: Most restaurant owners don't care if you're annoyed, as long as business is good.

The five restaurants we visited were all loud and all busy, leading Richard Peppin, an acoustical consultant and president of Scantek Inc. in Columbia to remark: "Noise has no effect on the commerce or the profit of the restaurant. I've been in 10 restaurants in the last two or three months. They're all noisy and people are still there."

"For some, the noisier the atmosphere, the better," said John Freytag, an acoustical engineer in San Francisco and an official with the Institute of Noise Control Engineering. "No one wants to be alone in a 'dead' restaurant. So high background noise for certain restaurants and nightclubs, with music often at the threshold of pain, is the goal."

Joseph Volpe, manager at Jaleo in Bethesda, told me he attempts to strike some sort of a balance. "We really try to have loud music," he said, "but this is as loud as it gets without complaints." It seemed pretty loud to me.

Both Peppin and Freytag have consulted with restaurant owners who have remodeled with acoustics in mind, but both agree there's not that much work out there. "Basically you'd probably starve if you did nothing but restaurants," Freytag said. Now there's irony for you.

Fact #9: Restaurant owners can minimize noise.

Better restaurant acoustics can mean tough choices for restaurant owners. They could go for people over profits by letting fewer diners eat at one time by moving tables farther apart or creating smaller rooms.

Or they could go for people over aesthetics by adding "acoustical absorption," which stops the noise from reverberating. A few examples: carpeting, heavy drapes, partitions, booths, upholstery, tablecloths, tapestries, acoustical ceiling tiles and the like. It would mean giving up the bare-ceiling, exposed-pipe look, the windows that are sometimes the size of walls, the exposed kitchens and the tile floors.

Or they could aim for some kind of happy medium. After all, aging boomers are still a big percentage of their customers.

Fact #10: Restaurant goers can make choices, too.

If you want to be out on the town, you have to make a choice: Either out yourself as a hearing-impaired person or out yourself as an older person. I don't see any way around it.

If you choose to be out about your trouble hearing, by all means, make yourself heard. At the risk of sounding crabby, ask the restaurant manager to turn down the music. Ask for a table away from speakers, heating or air conditioning units, kitchens and bars. Make it clear that you'd prefer to sit in a booth or against partitions and walls, particularly upholstered ones. And ask your friends to choose quieter restaurants.

If you would rather clean out your closets than admit your hearing loss to anyone but the CDC, then out yourself as a budding senior citizen. Tell your friends you don't want to fight for a parking space on Saturday night at 8. Instead, make a reservation for Tuesday night at 5.

It's much quieter then, and I hear the early bird special is to die for.

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Stefanie Weiss, author of the Health section's biweekly Midlife column, works at the University of Maryland's Academy of Leadership.