St John, who has previously overseen the Australian arms of several multinational record labels, is a casting consultant who has become a specialist in a new field: matching successful musicians to the television shows that crave their status, their experience and their celebrity. His marquee client is Channel Nine's The Voice, the hit reality singing show whose June finale drew a staggering national audience of more than 3.2 million people.

A major element in The Voice's breakthrough was the wattage of its judging panel: expatriate Nashville superstar Keith Urban; Australia's adult pop princess Delta Goodrem; Joel Madden, the frontman for American pop-punks Good Charlotte; and British balladeer Seal. As a group, they were strong enough to carry the show's launch marketing; as individual coaches they won over vast ratings.

''On The Voice, the coaches are the stars of the show,'' St John says. ''You're watching as much for what they say as what the contestants sing.''

Whether the discipline is singing or cooking, reality competition series have become some of the key television franchises of the past decade. One of the things that almost invariably separates the champions from the cancelled is the impact of the collective who pass judgment.

''It's very difficult for a show to work without the right judging panel,'' says Margaret Bashfield, who as executive producer of MasterChef Australia is able to rely on the trio of food critic Matt Preston and restaurateurs and chefs Gary Mehigan and George Calombaris.

''When you watch a show you want to enjoy the interaction between the people you're watching, and that's the special thing we have with our three boys.''

But as the genre has evolved there's been an escalation - slow at first, swift in the past few years - in the composition and cost of judging or coaching panels. Some people in the televisions business call it an arms race, and it went nuclear in 2011.

That was the year The X Factor here in Australia replaced shock jock Kyle Sandilands with former Spice Girl Mel B (Melanie Brown), who brought a large degree of likeability and 75 million album sales to the series. Brown went on to co-host another Channel Seven show, Dancing with the Stars, and her presence on The X Factor alongside Irish singer Ronan Keating added significant importance to the judging panel, which was then raised further by the launch of The Voice in America.

"There's always been a certain sort of person networks and production companies have booked for talent shows and without wanting to insult any of those previous people they aimed their sights a little lower - people with an industry background or who used to be a star," explains St John. "What changed is that there was a decision made to step it up and bring in superstar level talent."

The US version of The Voice put the multi-platinum likes of pop singer Christina Aguilera and Maroon 5 frontman Adam Levine in those spiffy revolving red chairs. That show's success, and the boost it provided to its judges' careers, meant that Ed St John was taken very seriously when he came calling on behalf of the local production.

''Part of it is that even the biggest music acts have to be broader in what they make their money from; they don't make it from record sales like they used to,'' he says. ''Part of it is that these shows don't damage the artist's credibility and, in fact, they introduce them to a huge new audience.''

A recent two-year stint on American Idol reinvigorated the career of Jennifer Lopez; Britney Spears is being paid $US15 million to sit alongside Simon Cowell on The X Factor; and chefs who successfully judge can find their reservation book quickly bulges. But those who assemble the panels insist you have to do far more than merely connect famous names.

''Machiavellian TV producers can cast as much as they like, but unless there's genuine chemistry there, unless something happens that transcends the sum of the parts, it doesn't work,'' Channel Nine director of development Adrian Swift says. ''You also have to cast for personality - in our case we had Delta, Australia's sweetheart, Keith was our professor, Joel was our clown, and Seal was our alpha male.''

Bashfield says her crew's MasterChef casting stories are ''legendary'', both for the number of people and mixes tried and the ease the chosen trio shared in front of the camera. ''It was extremely obvious when the right combination was found,'' she adds.

Still, issues remain in getting stars in the show's field to become nationally televised judges.

The medium's demands can be taxing, and the newly elevated can sometimes become overexposed as they grab every subsequent opportunity.

Just how rarefied the celebrity air prospective judges have to breathe might soon become known. The Voice has to replace Urban, who was so impressive he was poached to sit next to Mariah Carey on American Idol, and Channel Ten is rumoured to be opening next year with an Australian version of the successful British spinoff MasterChef: The Professionals. The names being bandied around to host the latter include superstar international chefs Gordon Ramsay and Heston Blumenthal.

St John says the dream team of potential music-show judges includes Robbie Williams, Rihanna and Michael Buble.

''I've made the trip to Katy Perry's manager's office several times and he's very nice about it but they say no to everyone,'' St John says.

But does the desire to net a Buble mean that mere experts no longer have a chance to be cast regardless of ability? Bashfield is adamant that if Preston announced himself now, he would still make the grade.

But former Australian Idol judge Ian Dickson, a record company executive who did the first of his five seasons on the show in 2003, doesn't believe he would get a look-in these days.

''I doubt it,'' Dickson says. ''Putting an unknown, slightly jowly 40-year-old British bloke on a judging panel was a big call, but that was 10 years ago. The judges have to have star power now.''

Still, the judge who successfully built the ''Dicko'' brand from scratch believes the securing of big names is just a trend, albeit a very expensive one with no end in sight. At a certain point, Dickson says, the viewing public's taste in judges will move on.

''The second someone breaks from the pack and does something different and it works,'' Dickson says, sounding just like a television show judge, ''I'll guarantee you everyone will think we no longer need superstars.''