Stellar students taught by the likes of Riggs, Stroud and their colleagues at Speech Level Singing International in California include Rosie Gaines, Michael Jackson (more of him later), Tina Turner and Stevie Wonder.

'Stevie was 19 when he got nodules [callus-like growths] on his vocal cords,' says Stroud, who was in Hong Kong last weekend to deliver a coaching seminar. Locally based instructor Christine Samson, whose Causeway Bay studio we're holed up in, is Asia's only qualified practitioner of SLS.

'Imagine having a guitar with one string, and all you can do with it is tune it up and down. You're constantly tightening up for the high notes and loosening for the low notes, over and over. Eventually something's going to happen to that string, and that's how Stevie got calluses on his vocal folds' - a pair of soft tissue cords joined at the front of the larynx that extend back.

To demonstrate, Stroud takes me through a scale on the piano, where I have to repeat after him. As he moves towards the higher notes, it feels as if someone is turning a screw, tightening my vocal cords. It's not long before my voice cracks under the pressure.

'So, Stevie went into surgery and had those calluses shaved off, before being told that he would not be able to perform for two years,' Stroud says. 'But after Seth Riggs taught him speech level singing, he was back on stage in three months.'

Good coaching is the difference between saving your voice and damaging it for life. Yet many pop stars would rather not shatter the illusion that theirs is a purely natural, god-given talent. 'Singers are afraid of new technique, not wanting to change their style,' says Stroud. 'And although we're like personal trainers for the world's greatest athletes, many are still reluctant for people to find this out. We have to sign so many secrecy contracts. There's so much that I can't talk to you about.'

It's little wonder that certain millionaire stars are unwilling to 'fess up, considering that this fledgling singer - whose boozy karaoke exploits have upset many ears over the years - found the introductory lesson pretty easy, all things considered. What magic did Stroud use to take my eeyore away?

'A bridge, or passaggi, is the point in your voice where resonation moves from one area of your body to another. The high note was resonating in your head as you sang it, but you strained, your voice flipped and the resonation went down to your chest,' he says. 'What SLS does is enable you to cross that bridge without tension or strain, giving you the ability to sing freely and go back and forth between the bottom and top notes.' In demonstrating this, Stroud makes the sort of sounds that unfortunately defy transcription.

He cites singers who have a tendency to use muscles that cause the larynx to move up in order to hit those high notes. This is known as 'pulling chest', and if not corrected can ruin a career. He picks out Liam Gallagher, of Brit-rockers Oasis, as an example. What was once a great rock'n'roll voice, with its sneering, crystal-clear delivery has been reduced to a throaty rasp, thanks to bad posture and technique. The ciggies, booze and drugs can't have helped either.

'He's totally trashed himself,' says Stroud. 'There's the lifestyle and the partying and then there's technique itself - the vowels are wide, the posture is all wrong, the neck is up, he's pulling his larynx up ...

'Singing is an athletic event. We're blowing air against these tiny pieces of tissue, it's a constant compression. If you do it right and don't abuse your body you can continue. Unless someone shows Gallagher how to look after his voice he will hit the wall and that will be it.'

Some might say Gallagher has already hit the wall. Michael Jackosn - aside from his present troubles and all the advice he could have done with years ago - did at least realise one thing: the importance of looking after his voice. 'I think it was his 'Dangerous' tour, and he was having trouble singing Dirty Diana,' says Stroud, who then begins to demonstrate with an intense performance, eyeballing me as he belts out the song.

'He was going 'Dirty Di - ana!' and in straining between the 'Di' and the 'ana' he was losing his voice. So we changed the emphasis on the vowels and that cleared it up for him. By changing it to 'Di-yana!' we created a bridge that he could sing through the middle of his voice without it flipping. Michael was making $1.5 million per show, so he couldn't afford to let people down.'

This isn't to say the technique is restricted to the famous, Many budding Hong Kong hopefuls subscribe to it. Nicky Hung Lik-hang, 23, has been studying for three months. 'It solved my problem in such a short time,' enthuses the singer, who has entered TVB contests. 'All I had to do was sing a few notes and my instructor immediately knew how to help me bridge the high and low notes.'

Rowena Fry, also 23, has been studying for 10 weeks, having returned to Hong Kong after completing a drama degree in Britain. 'I've already noticed that my voice is stronger,' she says. 'I used to get a sore throat from talking a lot, but that doesn't happen any more. It has also helped to increase my range - making it easier to manipulate my voice for different characters.'

At the very least, there are two people breathing easier, in more ways than one.