Which activity is restaurant noise a byproduct of, though? The servers moving between tables (in rubber-soled shoes)? Money changing hands (by credit card)? Pots and pans hurled by angry cooks (behind swinging doors or in an open kitchen where almost nobody speaks)?

What you hear in a packed downtown brasserie on a Friday night isn’t any of those things. It’s mainly the unamplified voices of customers fleshed out with amplified, typically recorded music. A few chefs and owners love to play their favorite music at teenage-Metallica-fan volumes but in most restaurants, the music is mere accompaniment to the crowd. Restaurants are loud because we’re loud. With a few exceptions, when we complain about the noise, we’re complaining about ourselves.

If you believe a restaurant’s primary function is to serve food, then it doesn’t make sense for us to respond by raising our voices. But we go out for other reasons. We go to look around, maybe to be noticed, usually to talk to the people we came with. Some of us want a drink or two, and almost all of us want to loosen the knots of tension that daily life ties.

Everything about the restaurant experience is designed to speed those things along, and when it all works, we respond by raising our voices. Far from being an accidental side effect, a noisy restaurant is the end product of a business that helps us have a good time, just as purring is the end product of scratching a cat’s chin the right way.

What makes a sound into noise is subjective. Just as a weed is a plant you don’t want in your yard, noise is a sound you don’t want in your head. Audio professionals call the sound we do want the signal. In a restaurant setting, we typically think of the signal as the voices of the people we are sitting with, plus the voice of any server who happens to be addressing us at that moment, but only at that moment. The minute the next table over wants help choosing the wine, the sommelier’s voice becomes noise.

Zeroing in on one voice in a room full of people talking is a complex job. When we’re young our ears are good at it, up to a certain volume, but we have more and more trouble with it as we age. Microphones are pretty bad at it, as every journalist who has recorded an interview in a crowded room knows. So are hearing aids, which amplify noise and signal equally, and can make a reasonably loud room seem unbearable.