Dialect coach Stephen Gabis has taught actors to mind their P’s and Q’s (and R’s and A’s) for dozens of Broadway productions, touring companies and movies. “Jersey Boys,” a musical about 1960s pop sensation Frankie Valli and the Four Seasons, recently opened in D.C., with Gabis to thank for the authentic working-class New Joisey accents.

Can you tell where people are from the second they open their mouths?
Yes and no. It’s not like a Henry Higgins party trick. There’s usually a few sounds I can use to narrow them down to parts of the country. In [New York City], they would say “Flarida, ahrange juice, hahribble,” so I can figure out they might be from around there.

How did you get into the business?
I was born in Brooklyn to a mostly Irish family, and I was always listening to all these exotic accents — my granny’s Irish friends and my dad’s mixed-up accent. I was an actor for many years, and the jobs came to me. I would be in a play and people would say, “Can you help us with the accents?”

Is it difficult to pick up an accent?
Not for me. I’m like a mynah bird. You’ll get actors who are very well-trained, and they know all these terms and they still sound like baloney. There are some horrible commercial tapes out there that people buy. And they’re all Lucky Charms Irish, cliche stuff based on cartoons and bad approximation.

Are there challenges specific to the “Jersey Boys” accent?
You get these 20-somethings from California or something, and when they hear the accent, they say “That sounds like Brooklyn!” Well, where do you think it came from? If you made some money in the 1920s or ’30s, where do you think you moved?

National Theatre, 1321 Pennsylvania Ave. NW; through Jan. 7, $61-$151; 202-628-6161. (Metro Center)