Whitney Houston will be remembered as a master of "melisma". But what is it and why did it influence a generation of singers and talent show aspirants?An early "I" in Whitney Houston's I Will Always Love You takes nearly six seconds to sing.
In those seconds the former gospel singer-turned-pop star packs a series of different notes into the single syllable. The technique is repeated throughout the song, most pronouncedly on every "I" and "you".
The vocal technique is called melisma, and it has inspired a host of imitators. Other artists may have used it before Houston, but it was her rendition of Dolly Parton's love song that pushed the technique into the mainstream in the 90s.
It can be heard in the songs of Beyonce, Christina Aguilera, Jennifer Hudson and others.
And anyone who has watched a talent show like X Factor or American Idol in recent years will have picked up on the trend among amateur singers.
The style became so prominent that former Pop Idol judges Pete Waterman and Simon Cowell had to ban aspiring stars from attempting to tackle Houston's hits on the show, Waterman says.
"It got so bad in Pop Idol 1 that we literally did say to everybody that walked in, 'Look there's no point in you singing Whitney Houston, so if you're going to sing Whitney Houston, don't bother singing, because we've heard it so many times now we're actually averse to it'," he says.
But the melisma craze isn't limited to contestants. Fame Academy vocal coach and judge Carrie Grant says her eight- and nine-year-old students come to lessons attempting to belt out their own takes on Houston's famous melisma.
"She started a whole generation of singers who wanted to riff on their records, and that includes all the Beyonces and the Rihannas and probably every American idol contestant," Grant says.
But most fail - miserably, according to Waterman.
In order to achieve Houston's vocal acrobatics it takes a combination of arduous training and natural talent.
"You can't do it without proper breath control, and that's the one thing that Whitney Houston had bags of," says professional opera singer Sarah-Jane Dale. "Let's face it, singers like that do not come along every week."
Houston also selected vowel sounds that would conserve air so she could hold the mammoth notes. For example, singing "luv" instead of "love", according to Dale.
And then there's the smooth, effortless sound of Houston's melisma - the result of using her body to control her voice.
"It's not just from your neck up. Singing is your whole body, and if you're not connected to that breath and where it comes from, down in your diaphragm area, you're not going to manage it," Dale says.
The vocal technique traces its roots back to Gregorian chants and the ragas of Indian classical music.
In the modern era singers such as Aretha Franklin, Ray Charles and Sam Cooke are credited with bringing melisma from the choirs of churches to mainstream audiences.
Mariah Carey's Vision of Love was a notable use. But it was Houston who popularised it and stretched the standards by attaching complicated strings of notes to single syllables.
But the term "melisma" is still relatively obscure within the pop music industry, with the effect often described simply as "ad libbing" or "riffing".
In less flattering terms, Rolling Stone's David Browne dubbed it an "overpowering, Category 5 vocal style" in the New York Times.
Singers can use melisma as a way of imposing their own personality on a song, according to Waterman.
"A part of this comes from the creative desire to do it your way and not the way the record company, the record producers and the writers are wanting you to do it," he says. "The writer has written you a tune, and you totally ignore it and do your own thing anyway."
Houston's shift from sticking to the song's parameters in I Wanna Dance with Somebody to taking vocal liberties in I Will Always Love You showcases this artistic transformation.
"I call it vocal gymnastics, where suddenly she wants to show you she can take a tune wherever she wants to take it," Waterman says. "The vocal performance on it is just mind-blowing, I mean everybody stands up and goes, 'My God, where did that come from?'"
But perhaps what Houston nailed best was moderation. In a climate of reality shows ripe with "oversinging", it's easy to appreciate Houston's ability to save melisma for just the right moment.
"She's like a cook who never overused her spice. She was always very delicate about what she would use," Grant says.
"She never oversang, and people, therefore, were touched and moved by the emotion and the story of that song. She's the singer that would give you goosebumps."