And speaking of the Simpsons

But then perhaps that’s only to be expected. After all, Cartwright, the 44-year-old mother of two who provides Springfield’s most famous son with his distinctive ""Ay, carumba!"", has much in common with her animated counterpart.

Back in the Capital for a second stint on the Fringe - she first appeared in 2000 - she admits: ""I am not shy, I am in your face, I will say what I feel like saying . . ."" Which all bodes well for a good interview.

Sitting in a coffee shop yards from the Assembly Rooms where her autobiographical one-woman show, My Life As A Ten-Year-Old Boy, is running, the actress produces a flier from her bag and muses: ""I guess the show is best summarised as a romp through Springfield via Dayton, Ohio. In other words, it’s my life through my eyes and is about the decisions I made along the way to get to where I am.""

Cartwright, once the voice of Gutsy in My Little Pony as well as Bart and a host of other Simpsons characters and ""fraidycat"" Chuckie in Rugrats, made one of the most important of those decisions back in 1987.

Already an established voice artist at the time, she was approached to play a role in a series of occasional cartoon sketches for the Tracey Ullman Show.

Cartwright recalls: ""When I was told that it was to do a voice for this little vignette on The Tracey Ullman Show my attitude was, ‘Who cares? Who do they want me for?’ ""

She discovered that they wanted her for the middle child, Lisa Simpson, and she admits: ""I was a bit snotty about it because at the time I was doing eight other shows and was already successful in the industry. But it was work, so I went for it. Basically I went in for the girl and ended up with him [Bart] and that was my choice.""

It was a choice that would ultimately allow Cartwright to fulfil an ambition that first began to germinate when, at the age of ten, she won an elementary school public speaking contest in her home town of Kettering, near Dayton, Ohio.

""That gave me an idea, not about voices but about entertaining,"" she explains. ""I recited Rudyard Kipling’s How The Camel Got His Hump and it made people laugh.

""It wasn’t even necessarily my voice that made them laugh, in all honesty. It was the way I delivered it. But it made the kids in the audience laugh and I guess that’s why I won.

""But it also did something to me that made me think: ‘Oh, I like that. I like creating that effect, making people laugh’. So I started to pursue other opportunities that would allow me to do that.""

By the age of 16 Cartwright had decided that a career as a voice actor was the one for her. ""I got a job in the trafficking department of a radio station, scheduling the commercials,"" she reveals. ""One day a woman from Warner Bros visited the station and my boss, who knew that I was interested in doing voices and possibly cartoons, introduced me to her thinking, like me, that Warner Bros meant Mel Blanc - Daffy Duck, Bugs Bunny. She couldn’t help but gave me her card and said: ‘Write me a letter and I’ll get it to someone who can help you’. She was true to her word and sent me a list of names and phone numbers. One of them was Daws Butler who, her letter said, was the voice of Roadrunner - I thought: ‘Roadrunner doesn’t have a voice’.""

Doing a bit more research Cartwright discovered that Butler was also the voice of Huckleberry Hound and Yogi Bear.

""I called him and got his answering machine. He had recorded a message as a very stodgy British butler. So I did this kind of cockney voice and it worked. He called me back and that was the start of our relationship. Within 20 minutes he had agreed to send me a script and a tape and offered to listen to my voice if I put it down on a tape for him.""

Butler became her mentor and when Cartwright moved to Los Angeles shortly after the death of her mother, Butler and his wife ""adopted"" her.

Fondly she recalls: ""They had four sons, they didn’t have a daughter and I kind of fitted in as the baby of the family. Every Sunday I’d take a 20-minute bus ride to his house in Beverley Hills for a one-hour lesson and be there for four hours.""

Sadly Butler died shortly before Cartwright first voiced El Barto, the kid who would make her a household name, if not a familiar face. That anonymity, she reveals, can be a mixed blessing.

""Here we are sitting in a coffee shop in the centre of town and nobody knows. They have no clue who I am. The anonymity factor is built in and I love it.

""For example, before coming to Edinburgh I was in London, a stranger in a strange land. I needed some cash so I went to a cash machine, put my card in and put in the wrong pin number three times in a row. I messed up. The thing ate my card.

""It was late and the bank wasn’t open so, first thing next morning, I go to the bank. I go to the clerk. He looks at me like: ‘Sorry lady, I can’t help you,’ when my friend leans over and says to him: ‘I don’t think you understand who you are talking to. Are you a fan of The Simpsons?’

""I’m like: ‘Oh my God, I can’t believe she’s doing this’. But you know what, it worked. The clerk looked at me and said, ‘I’m a huge fan’. And I said: ‘Hi I’m Bart Simpson, what’s happening man? What kind of ID do you need, nobody else does this voice’.""

The transition from 40-something mom to ten-year-old boy is instant and seamless.

""Bart is so easy to do that I don’t even think about it,"" she says as a police car, with siren howling, screams past the window. ""Busted. Guilty as charged,"" chips in Bart, before Cartwright continues, oblivious to the puzzled glances from her fellow coffee drinkers: "". . . no, Bart is easy, but I also do Nelson Muntz on the show. That’s tough because he’s very gravelly and if he’s heavy in the show I’m tired by the end of the day and my pipes are a little worn out, although they do heal overnight.

""It’s all about placement of the voice, which is difficult to describe, but, for example, Ralph Wiggum is heady, whereas Nelson is throat and Bart is a bit . . . I don’t know where he is. That voice came first time.""

That voice also won Cartwright an Emmy Award for Outstanding Individual Achievement in voice-over performance, one of many Awards the show has garnered over its 16- year history. But not everyone is a fan.

""I overheard a conversation once that really got me,"" says Cartwright, a mischievous twinkle in her eye. ""It was at a track meet where my son was racing. I was by myself, sitting behind a group of people and they were talking about television and one of them started being a bit critical about The Simpsons.

""So I tapped her on the shoulder and said: ‘Excuse me, I couldn’t help but overhear what you were saying. I’m a mom too, and as far television goes . . . yeah, but I have to let you know, I’m Bart Simpson’.""

Fleetingly Bart’s back, before his creator continues: ""She looked at me and I’m sure it embarrassed her but people who criticise The Simpsons don’t watch the show - and I was right, she didn’t watch the show. She’d heard about it and seen some of it.

""Yeah, Bart says bad words and he’s not a good role model, but is that his purpose? No. If he was a good role model we wouldn’t have a show. It’s a Greek drama. You have to have a protagonist and antagonist and a whole citizenship - the people of Springfield.""

While My Life As A Ten-Year-Old Boy will be the highlight of the Fringe for many fans of The Simpsons, Cartwright herself is looking forward to being joined by her children, 14-year-old Lucy and Jack, aged 12, who are flying in to the Capital to catch the end of the run. But what do they make of her line of work?

""They grew up with it, so they just take it in their stride, but I am the most popular mom at school,"" she says happily. ""All I get is ‘Do Bart, do Bart!’ "" - ""No way man"", he’s back again.

""I never say anything when they change schools, but in time it leaks out and I start getting these looks from the kids and I think: ‘Oh, he knows, and she knows . . .’

And what if Bart were ever to be killed off? As a voice artist do you become as attached to a character as an actor might in a sitcom?

""I didn’t have any sense of loss when I stopped doing My Little Pony,"" she says roaring with laughter. ""It was okay to say goodbye to Gusty. But to someday think that I’m not going to be doing Bart again . . . I don’t go there.""

Assembly Rooms, George Street, until August 30, various times, 13-16.50, 0131-226 2428"