She's like a big, black, smiling sun; her voice seems polished by the sea, weathered by the wind, and is at once earthy and unearthly as she sings of the pain of love and the consolation of the divine. Ever since she brought her army of samba greats to the Royal Albert Hall, Virginia Rodrigues has herself been a divinity - a status sure to be confirmed when she sings at the Queen Elizabeth Hall next week. Brazil has never produced a voice like hers before - and the rest of the world has never heard one. Unadorned purity is only part of it: the magic resides in how she uses that quality to express the savage realities of her early years.
My first encounter with her was in a ramshackle theatre in the colonial heart of Salvador. She was part of an amateur theatre group run by the avant-garde guru Marcio Meirelles, and while her colleagues cavorted athletically around the stage, she simply sat in the middle and sang. Everyone involved knew that she was a star, though at that time her name was completely unknown. Whenever she opened her mouth, the actors faltered in their stride, arrested by the beauty of her sound. The production's Yoruba title, Ere, reflected both the performers' roots and their subject matter, since Ere is the name of a playful spirit who appears during the transition between possession and the return to normality in the Yoruba Candomble ceremony. The play, she told me, was a Candomble prayer for the local street children who were at that time getting picked off by trigger-happy police. Rodrigues hadn't been a street kid, but she was born in a favela, and she'd recently embraced the Candomble faith: she knew what she was singing about.
Even today, Meirelles talks with bemusement about how he found her. "It was the feast of St Anthony, I had nothing to do and was just standing in the street, when I heard this amazing sound coming out of a church. I went in, and there she was, standing alone in the centre of the nave - and I found myself crying. So I went up to her, took her hand, and asked where she'd got her voice from. She laughed and said she didn't know."
He'd been trying to devise a conclusion for a play about Salvador's regeneration with the Bando de Teatro Olodum - later to star in Paul Simon's The Rhythm of the Saints and Michael Jackson's "street kids" video - and this meeting with Rodrigues gave him the necessary inspiration: she would spend all evening sitting on stage like a deaf-mute, and finally burst into song. The result, he said, was an audience in floods of tears. Then a showbiz miracle occurred: Brazil's foremost singer-songwriter Caetano Veloso, who happened to be present - and who was likewise moved - offered to record her. And the rest is history.
Rodrigues - who once sardonically itemised her disabilities as "I'm a woman, I'm black, I'm poor" - looks back with affection on her early days in this "black Rome" where she still lives. "My favela was called the Seventh of April, and as everyone knows, people who lived there didn't have many chances in life - to survive was an achievement. But my childhood was good - I sang and danced all the time, to the music on the radio. All I wanted to do was sing, so I began performing at wedding parties and jubilees."
While working as a cleaner and washerwoman, she joined a convent choir, attended free singing workshops at Salvador University, and began to define her own talent in relation to the great singers from whose careers she drew inspiration: Billie Holiday, Ella Fitzgerald, Aretha Franklin, but also classical divas such as Jessye Norman, plus Brazilian singers galore. "The magnificent Gal Costa, Maria Bethania, Clara Nunes, and many more. I admired them all, but never wanted to imitate them. I had to do it my way."
Her way of singing might send conventional voice coaches rigid with disapproval, but it's as natural as breathing, and Mares Profundos - the album she's just released on the DG label - shows it off to perfection. This is a cycle of "Afro-sambas" created in the Sixties by the writer Vincius de Moraes and guitarist-composer Baden Powell, which marry the laid-back elegance of bossa nova with devotional lyrics addressed to the Yoruba saints that are ubiquitous in Salvador. To these songs, as the South Bank audience will discover, Rodrigues brings her own special vision.
But it's not a vision in the literal sense of the word. "Candomble may be my religion," she says, "but I don't think about it when I'm on stage. But before I go on, I always ask for the gods' protection - as I do for everything else I do in life." Some of these songs are bleak and desolate, some are jauntily combative, and many - particularly those that address a divinity by name - radiate stately awe. When I ask the meaning of her final track - a wordless vocalise entitled "Exu's Lament" - she gives a suitably arresting reply: "It reminds me of the Wailing Wall in Israel, where people go to weep. But I don't know what the song is about - it's just a lament for its own sake. And a plea for help."
Virginia Rodrigues plays the Queen Elizabeth Hall, London SE1 (0870 401 8181) on 18 March at 7.30pm