She just stood up and sang the song, lifted it a few inches off the ground and off she went

Dave Gelly Jazz critic

"I didn't know what I was. I just liked to think of [it as] interpreting," she told an interviewer in 1988.

But she was the greatest white female singer of the 20th century and the female equivalent of Frank Sinatra, according to Observer jazz critic Dave Gelly.

She had a "very simple, low key" style in which her immaculate timing was key, he told BBC News Online.

"She could really just hit it in that way that really good jazz singers can," he said.

Lee sang at Louis Armstrong's funeral in 1971

"She didn't do it by changing the songs, she didn't alter the tune, she didn't skat.

"She just stood up and sang the song, lifted it a few inches off the ground and off she went. Beautiful, just gorgeous."

Louis Armstrong once told her: "Peggy, you can swing better than anybody I know at the drop of a hat," according to Mr Gelly.

Her popularity was at its height in the 1950s and 1960s, earning her a Grammy in 1969, while she was also an accomplished lyricist and actress.

"In the 1950s, a Peggy Lee album like Jump for Joy, or The Man I Love, which Sinatra conducted the orchestra for, would sell phenomenally around the world," Mr Gelly said.

"She made one of the early concept albums, too, called Black Coffee, which was basically the ruminations of a deserted woman sitting at home thinking over her life."

Madonna shares Lee's skill for reinvention

Very few current singers directly copy the Lee sound, Mr Gelly said - but her simple style has become absorbed into the general currency of jazz singing.

"The ones who just sing the song straight - there's a lot of Peggy Lee in all of them," he said.

Modern stars including kd lang, Diana Krall, Carly Simon and even Madonna have all said they are fans.

Madonna is the closest we have to a modern equivalent of Peggy Lee because they both had a gift of reinventing themselves, according to Lucy Powell, author of The Making of Miss Peggy Lee.

'Breathy intimacy'

"If you think about the fact that Peggy Lee sang with the likes of Duke Ellington, Benny Goodman and Paul McCartney, she was able to reinvent herself with every decade," she said.

But Lee could do more for a song by "a mere rolling of her eyes or with a quick, crooked smile" than most pop singers could with years of training, another critic, John Seagraves, wrote.

The singing voice that gave her tunes a "breathy intimacy" was her greatest asset, says Pete Marsh, jazz specialist on the BBCi Music website.

"The thing about her was that she was extremely understated. That was her gift.

She does not carry a tune, she elegantly follows it

Whitney Balliett Jazz critic

"She was completely unpretentious - not a showy singer like Betty Carter or Ella Fitzgerald. She was technically gifted, but she didn't show it off as much as they did.

"She had this kind of up-close and personal style, which meant she could cross over into the mainstream more than many of the others."

As The New Yorker's legendary critic Whitney Balliett once wrote: "Many singers confuse shouting with emotion. Peggy Lee sends her feelings down the quiet centre of her notes.

"She does not carry a tune, she elegantly follows it."