Now, it's almost entirely audience-driven.
Media brand consultant and owner of Third Wave Media, Eriks Celmins is regularly brought in to consult with Kiwi radio stations on what goes to air.
According to him, songs get on the radio through three major routes: the labels, the online buzz, and the old-fashioned breakthrough.
Record labels meet with radio stations regularly to pitch new tracks and artists on their rosters. Within this, of course, new offerings from superstars -- think Taylor Swift -- "are very efficiently delivered", and pretty much guaranteed to hit the airwaves immediately.
There's also still the opportunity to break through independently, although you can't just submit a demo and hope for the best. Celmins says hopeful artists must deliver a full package -- plan for releases and marketing, a fully-fledged online following complete with analytics, the lot.
But what's really changing the game is the internet.
"Mainstream pop culture moves so fast, there are so many different ways you can be exposed to music. In earlier times, radio was one of the main things that really could make or break songs, because there wasn't much other choice," Celmins says.
"Now you can stream, download, YouTube, get recommendations from friends sharing songs and playlists and that's really healthy -- it's a great incentive for radio stations to keep an open mind."
Stations are monitoring Spotify, online charts, YouTube, trending content, and even Shazam to get an idea of what's taking off. After that, it's up to them to make the call as to whether it gets air time, and as Celmins says: the stations that take the risks "tend to win".
And when all that's said and done, the songs are subject to market research, thrown into a survey each week and ranked by listeners who participate for a chance to win prizes.
ZM is one of the biggest radio stations in the country, and their music meeting is done and dusted in minutes -- the decisions are made quickly but they're well-informed.
Research results for the week are made up from the feedback of 100-150 listeners who have listened to 8-second snippets of about 40 songs.
There are different columns for positive, negative and neutral feedback, one which gauges a song's potential, whether people are getting sick of hearing it, whether people haven't heard it enough, and some of those are broken down again to reflect the feelings of different age groups.
From there, content director Ross Flahive and his team can pick out which songs need to be dropped, which need to be played more or less, which need to play at different times of the day, and where there's room to introduce new content.
At that point, they have a quick listen to their pre-filtered "priority tracks" and make a black-and-white call as to whether it makes the cut for their listeners or not.
Everything boils down to the audience.
At a more specialised level, like hip-hop station Flava, it's a similar story, though with important differences.
Flava's content director Hayden Hare says his major issue is hip-hop as a genre is notorious for a fast turnover -- artists are constantly releasing new music, and a lot of it unofficially.
Add to that, the fact that hip-hop artists tend to feature on each other's tracks, and that creates the potential to oversaturate the airwaves with the same few voices.
But there's also a lot more room to move. Hare spends his spare time trawling through hip-hop sites like Newmusicserver.com, digiwax.com and mixshowtools to find the next big thing before anyone else, and works closely with local artists to make sure Kiwis are getting their fair share of airplay.
We quite often have songs that go off here [in New Zealand] that weren't big anywhere else.
But he also has the liberty of playing his back catalogue for an audience that loves hearing the "throwbacks".
"We quite often have songs that go off here [in New Zealand] that weren't big anywhere else -- Riding Low by LAD, Return of the Mack by Mark Morrisson, This Is How We Do It, by Montel Jordan -- there's a longevity thing here, we hold on to those records," he says.
Once they figure out which songs make the cut, they're put into a rotation. More popular songs will rotate more often, while less popular songs will only crop up every now and again until they take off, or get dropped.
That's why, when you turn the radio on throughout the day you end up hearing the same songs over and over.
As Flahive puts it, most people are listening to the radio only once or twice a day -- not many people would listen to the same station all day, and most people are listening at peak times: breakfast, and on the drive home from work.
The radio stations have to be picky, too, because they also have to pay two fees for every song played -- one to APRA on behalf of the writer of the song, and one to Recorded Music NZ on behalf of the recording of that song.
That fee is a percentage of each station's advertising revenue -- changeable depending on how big the station is and its broadcast size, relative to how much advertising it draws in. ZM, for example, pays 6 per cent of its revenue each year.
In Australia, APRA AMCOS pin-pointed an average fee for a metro radio station to play a single song, at around $6.
And with most major music stations playing approximately 215-250 songs in 24 hours (Hare says Flava's playlist includes about 260 songs), the fees could stack up as high as $1500-$1600 a day.
So with that kind of money at stake, no decision is taken lightly and not only that but Celmins says they have to "move quick" on new songs and make the right call or suffer.
"Because pop culture's changing so fast, if everyone else picks it up and you miss it, your ratings suffer," he says.
It sounds cut-throat and as if there's a lot of room for error, but Celmins says rather than making content directors' jobs harder, the new way of working is actually a good thing.
"When you have your target audience voting on a list of songs and there are songs at the top of the list, they are going to get played. Just like songs at the bottom list are likely to get dropped like a hot potato," he says.
"So it's actually very democratic. I think it's great."
