Together with her husband, the conductor Richard Bonynge, she had one son, Adam, who was born in 1956.

Adam's wife, Helen, said last night her mother-in-law would leave a significant legacy.

''She's a very important person all over the world, but for us this is our family and we're just trying to come to terms with this,'' she said. ''She's had a long life and [gave] a lot of pleasure to a lot of people.''

Sutherland and Bonynge - a power-couple of Australian classical music - retired to the resort town of Les Avents, near Montreux in Switzerland, and she has made few public appearances in recent years.

Lyndon Terracini, the artistic director of Opera Australia, said not only was Sutherland the greatest operatic singer Australia has produced but also one of its most generous and supportive ambassadors of the art form.

''I got to sing with Joan at a number of operas at the Sydney Opera House when I was in my 20s and she was always an interested, open and generous colleague. She was not all protective of her turf.

''When she retired from the stage, she was already a legend and no operatic singer including Melba, in my view, has had that impact, not only in her own art form but to the general public.''

She sang in an estimated 265 performances of 23 different roles with the Australia Opera, but it was Norma that was her seminal work.

The American mezzo-soprano opera singer Marilyn Horne was watching in the wings when she performed Norma at the Opera House.

She always knew Sutherland had one of the great voices in the world but she was reminded why she was so legendary: ''She had one of the most formidable vocal techniques of all time: she was able to get through one of the most demanding roles in all opera using mind over matter and giving us all a lesson in superb technical singing.''

It was a performance revered not only by Horne but also by Kiri Te Kanawa, who would be equally inspired and become one of Sutherland's friends.

Friends and colleagues last night could not speak more highly of her.

''I think she was undoubtedly one of the most unique voices that one is ever likely to have heard and certainly one of the greatest voices in the history of opera,'' said a former artistic director of Australian Opera, Moffat Oxenbould.

''She had an extraordinary professional ethic … She was a very loyal friend, she was somebody who loved being part of a company … she rehearsed when it was necessary all day, all night, she knew the name of everybody with whom she worked. She was just Joan,'' he said.

The president of The Joan Sutherland Society of Sydney, Doug Cremer, said: ''All I can say is that she was the most unassuming, genuine and generous person I've ever met.''

Although loved by most Australians, she did attract the occasional controversy.

In 1994 she addressed a lunch of 250 staunchly conservative Australians for a Constitutional Monarchy in Sydney, telling them she still called Britain home, missed her British passport and was not pleased to be interviewed by a ''Chinese or Indian'' to get an Australian passport.

Sutherland was nicknamed La Stupenda by an audience at Venice's famous La Fenice opera house in 1960 after a performance of Alcina.

Montserrat Caballé´ described the Australian's voice as being like ''heaven'' and Luciano Pavarotti once called Sutherland the ''voice of the century''.

http://www.smh.com.au/entertainment/opera/the-voice-of-a-century-dead-at-83-20101012-16g8q.html