Being Portugal's number-one cultural export must be a tiring business. Mariza Reis Nunes - fadista (fado singer), fashionista and Unicef ambassador - sounds shattered when I talk to her in her Lisbon home. But she's still warm and articulate, answering my questions in her poetic broken English without a hint of complaint. Doesn't she get sick of talking to all those Portuguese embassy staff, music business hangers-on and journalists? "Oh, no, no, no, I love that," she says, sweetly.
The past five years of her life have been a steep and steady career trajectory. Her 2001 debut, Fado em Mim, marked her out as the leading voice of a generation, reviving Portugal's urban folk-song tradition, fado - an understated, melancholic, acoustic music sometimes dubbed the "Portuguese blues". That record launched her European career in style, but it was her third album, Transparente (2005), that saw her go global.
Drafting in the acclaimed Brazilian arranger/producer Jaques Morelenbaum to graft velvety orchestral arrangements on to her intimate but intense songs was a risk that paid off handsomely. Traditionally, fado is almost always sung with just acoustic guitar, the distinctive chiming sound of the 12-stringed guitarra Portuguesa, and, more recently, bass. Fado icons of yesteryear such as Carlos do Carmo and the late, great Amalia Rodrigues - to whom Mariza was, inevitably, compared early on - broke out of this musical straitjacket in a similar way, sometimes with cheesy consequences.
Nowadays, those Amalia comparisons aren't so prevalent as Mariza is recognised as a star in her own right. "I don't walk around now too much. It's impossible now, almost - we start having paparazzi in Portugal and sometimes they give you a hard time," she laughs, huskily.
But it doesn't stop her going out at night, and on the rare occasions when she's in town, you might still bump into her in one of Lisbon's small, atmospheric fado houses.
It was at one such place, in the waterfront neighbourhood of Alfama, that I heard Mariza sing, early one spring morning in 2003, just before the release of her second album, Fado Curvo. There were no more than 10 people left in the club, but her performance was as dramatic as at any big concert hall. The songs seemed to possess her, a passionate flurry of involuntary gestures marking each denouement. Even more striking was the sheer volume of her unamplified voice - more than twice as loud as any singer we'd heard that night.
"I have an amplifier - when I was a child I eat one!" she jokes. "I don't know how it happens, really. I never have music classes. I use it as the way I learn on the street."
Mariza was born in Mozambique, but when she was three years old, her Portuguese father and African mother moved the family to Lisbon's historic Mouraria neighbourhood, where they ran a restaurant that was a regular haunt of fadistas. As a child, Mariza would occasionally sing fados there, but also with friends in the narrow, cobbled streets. "I think it was a kind of exercise, maybe, to make me have a stronger voice. If my neighbour wasn't listening to me in the third floor, I was dying, you know, I was ashamed."
Aside from her stunning looks and fashionable style, Mariza's take on fado is subtly different from that of her contemporaries, distinctly reflecting her African heritage. Most traditional fado uses the bass to "secure" or support the acoustic guitar, which provides the main melodic line. And the Portuguese guitar "answers" the singer. In Mariza's music, the bass and acoustic guitar have different roles.
"For me, the acoustic guitar is the one who give me the floor. I can walk. It's my support. Then, the bass is the one who give me the rhythm. And then the Portuguese guitar is the one who answer my voice. Fado has lot of rhythm. I listen to a lot of African music and Brazilian music for many years, and bass is one of my favourite instruments."
What flows naturally from that also sets her apart: she dances. "Hmmm, no. I think I don't dance, I move," she chuckles. "Normally, fado singers don't move, they sing still, and I have that bad habit of moving! When I start listening to music, I start moving, even if it's classical. The other day, I was at the opera, in Thailand, and I was beating my feet. Everybody was looking at me like, 'What's she doing?', and I was like, 'Oops', you know, because I'm feeling music. When I'm on stage, that happens, too. I can't sing still."
Mariza has just returned from a sold-out whistle-stop tour of Asia, where crowds responded with standing ovations. "They are understanding the music, they are crossing frontiers and feeling the music. That's amazing. The language is not so important as people think," she observes. Even though Portuguese speakers can appreciate the poetry of fado lyrics, the music's real language is emotion - something that Mariza's extraordinary voice conveys effortlessly. But how important are the words to her?
"Without good poetry, or good lyrics, it is impossible to have a meaning to sing. Because you are telling a story. When you sing poetry, you are releasing feelings. They're going to understand what I'm feeling even if they don't understand my language," she explains.
After talking to me, Mariza has to rush off to a radio interview, tour Belgium, and rehearse for her show at the Royal Albert Hall, the star attraction in London's annual Atlantic Waves festival of Portuguese music. "I always thought for me it would be impossible to do a place like that, with such a big history, where the best singers sing, for my style of music, it's a kind of dream come true."
It won't be her biggest-ever gig, though. In September 2005, she sang to 25,000 adoring fans, backed by the 30-piece Sinfonietta de Lisboa, a show captured in miraculously detailed sound and vision on her new CD/DVD Concerto em Lisboa. The Albert Hall concert will feature the London Session Orchestra, conducted by Jaques Morelenbaum, plus special guests Carlos do Carmo and the Cape Verdean singer/ songwriter Tito Paris.
"I want to show people the three faces of the triangle of Lusophonia. Fado has the Portuguese, and we are there. Fado has the Brazilian face, and Jaques is there. And fado has the African face, and Tito is there, bringing the Cape Verdean morna, and showing it is not so far from fado as people think."
As for future recordings, is she planning an album of "Lusophonia"? Maybe. Will she record something in English, such as the version of "Fly Me to the Moon" that she sang on Jools Holland's Later... show last year? Unlikely. "I don't have plans yet. I'm very in the mood of giving another step in front, but at the same time, I'm very much in the mood to something very traditional. I'm a little bit confused, so I don't have a clue.
"I'm researching already, about poems and everything, and I'm going to stop for six months to work on a new album. But now is not the time for stopping."
Mariza will appear at the Royal Albert Hall, London SW7 (020-7589 8212) on 22 November; 'Concerto em Lisboa' is out now on EMIReuse content