The next three minutes could he the most important of your career. After months of rehearsing, recording and gigging, your music is about to he put to its final test: over the airwaves.

BEFORE THAT INVISIBLE LINK is made between musician and listener, discussions and meetings have taken place, decisions and payments made. How does your act, as opposed to the hundreds of others all vying for the attention of radio stations, get its music on the air? Let's examine the process by which you can gain that essential exposure - airplay.

For the majority of new bands, the starting point will be a session with a local BBC radio station. While daytime programming is almost always orientated towards chart music, most stations have some kind of specialist evening programme playing music from outside the charts and willing to showcase local bands.

At BBC Radio Leeds, for example, the show that matters is 'Great Northern Rock'. Broadcast weekly in conjunction with Radio Humberside and Radio York, the show features a local band playing live from the studio in three slots of two tracks each. There's also a live-minute interview with the band. As presenter Jan Bers says, "probably the best experience you will ever get is to do a live broadcast."

Sessions normally arise as a result of demo tapes being sent to the programme, though the show's presenters also do a certain amount of talent-spotting at local gigs. As always with demos, the presentation of the tape is often as important as the sound quality. Though no-one expects the tape to be perfect, it must attract attention and be listenable.

If you're booked for one of these live sessions, you'll be asked to submit an equipment list and a rough duration of the tracks you wish to perform. On arrival at the soundcheck, equipment is tested for earthing and levels set. One of the songs is taped in advance so that you have some say in the broadcast mix. Because everything is going out live, there is a "panic button" should disaster strike.

After the session, you'll be given a tape of the performance and expenses. The radio station keeps a copy of the session tape for library purposes, and this may be used in repeat sessions.

Across the Pennines, Radio Piccadilly serves some three million listeners in the North-West. As one of the nation's five largest independent stations, it uses a different set of criteria with regard to sessions, as Head of Music Robin Ross explains. "When I came to Piccadilly I found they were encouraging a lot of local talent, but it might not be good quality. If you were in a local band you got a session and it was played once on a Sunday night. To me that meant two things: first that we weren't looking for the right local talent, and second that we were wasting our money, because we get five plays on it and it was only being played once."

Ross' answer was to invite national as well as local artists to record songs in a Manchester-based 16-track studio for the station's exclusive use. Fees for these sessions are set by the IBA's radio committee and work out around £80-100 per band member. The rights to the sessions belong to the radio station and the station may broadcast each session live times.

Recently, Piccadilly have recorded sessions with such acts as Hothouse Flowers, Deacon Blue, Mica Paris, Julia Fordham and Maxi Priest. These sessions are played throughout the day and introduced as music "specially recorded in the North-West" for the station.

Ross is keen to encourage local talent, but on his own terms. "I'll offer bands a session at any stage in their career", he says. "They don't have to have a record deal. If I hear a tape and like it, we'll go with it. I know people will argue that 'we live in Manchester and we deserve this, if you've only got so much money to spend then we should have it'... Well, if the talent is good enough, they'll get it."

Along with other large commercial stations and Radio 1, Piccadilly runs specialist programmes outside of peak daytime programming. It's true to say that as the audience figures fall, so the programming becomes less rigid, offering more opportunities for the showcasing of new talent.

Sending tapes to these "minority audience" radio shows has always been worthwhile for young bands anxious for their first taste of the airplay cake. Nationally, the obvious example is John Peel's show on Radio 1.

Peel and producer John Walters receive about 200 tapes a week, and try between them to listen to every one. Peel's programme plays between three and five sessions from new bands every week. And in fact, it's true to say that almost all the important acts of the last two decades have featured in Peel sessions, as have many other bands that have since vanished into complete obscurity.

Changes in scheduling for night-time Radio 1 have just taken place, however, and it's not yet clear how these will affect the session situation. Theoretically, the new two-hour extension (until 2am) will open up more opportunities for new bands as both Nicky Campbell and Richard Skinner will be playing sessions, but their taste may not be as eclectic as that of Peel, who has moved to an 8.30 slot.

If you get a session on "Britain's favourite radio station", Radio 1 will retain the rights to repeats of the material, but won't actually guarantee you a repeat spot. A spokesman for the station says that "the decision to repeat a session isn't necessarily in our hands; it depends on whether there's a developing interest in the band and things like that."

It's unlikely that a session recorded for one show will be used on a different programme, and Radio 1 never uses sessions as part of daytime programming. Sessions are undertaken for a nominal fee, though Performing Rights Society membership (if you haven't got it, get it) will secure the writers or publishers of songs a royalty for their use.

Daytime programming on both ILR stations and Radio 1 revolves around the playlist system. At Manchester's Piccadilly, two systems are in operation thanks to the split-frequency broadcasting that has enabled the recent launch of "Key 103" on the station's FM bandwidth. The medium-wave (AM) station now operates as "Hit Radio", with a playlist comprising the independent Network chart and up to 25 new releases, usually from bands with a previous hit record, and played in strict rotation throughout the day. The remainder of airplay is taken straight from the Guinness Book of Hit Singles.

Key 103 offers a different service, as Robin Ross explains. "The Key 103 music policy is that a record doesn't have to be a hit single, it can be a 'Key' record. We have adopted a system of classics and 'recurrents', the latter being hits of the last 18 months." To this is added a contemporary list of chart singles and album tracks, but none of the novelty and bubblegum hits that regularly chart - these are deemed too immature for what is seen as an older and more "discerning" (read "wealthy") audience.

"The singles market is plummeting", says Ross, "and I don't believe it is the way forward for radio - that lies in Compact Discs, albums, and quality singles."

As Head of Music, Ross draws up the playlists himself. At Radio 1 the lists are decided by a committee. This is made up of seven members: the producers of the daytime shows and playlist head Chris Lycett, all of whom have a vote. Radio 1's Head of Music, Roger Lewis, attends on behalf of the management but doesn't hold a vote. Similarly, DJs may also sit in without a vote, and can - if time allows - put forward records for playlist consideration.

Records may fall off playlists quite quickly, depending on what singles are coming out. Programming is balanced to avoid a glut of similar records appearing at once, so that - for example - a dancefloor record may be held back if there are already too many dance cuts in the charts. Playlist members are also given a brief to favour new British bands if they have a particularly strong single out.

A spokesman for Radio 1 comments: "A new band who make it to the playlist have in a sense got it made", and there's not much more to be added, really. With such power over the future of a new release, playlist committee members are the target of the "pluggers". Radio 1 recognises certain people as record pluggers, and these people are able to get appointments with playlist producers to promote their products to them.

Scott Piering is an independent plugger working exclusively in London-based radio. He describes a typical plugging appointment at Radio 1 like an American Football coach describes his game plan...

"I've prioritised my records already. I lead with my strongest because I want a positive reaction, I want it to set the stage for the next one. This is probably as good as the first, but by a newer group with less profile. Perhaps it's slightly poorer production-wise. As a third record I will have a coat-tail record which is worth exposing the producer to for the name to get across, though it's not the group's hit, and to give him an idea of what their music is like."

Pluggers must have faith in the product they are promoting, and to an extent they must also know what is likely to please the people they are playing it to. Not all pluggers are satisfied with the medium they work within. Tony Michaelides works throughout the ILR network and has an artist roster which includes New Order, Steve Winwood, Julia Fordham and S-Express. Of the playlist system he says: "It's a dreadful position to be in. A number of middle-aged men at radio stations are really responsible for your career; they govern the tastes of the nation. If they don't play it the public don't get to hear it and are unable to make their own minds up. It's a constant uphill struggle, but from a radio station's point of view, they must have a station sound and a targetted audience."

With any luck, the forthcoming deregulation of radio - which Piccadilly's Key 103 and Radio 1's night-time shuffling are designed partly to guard against - may diminish the importance of playlist committees, pluggers, and the whole sordid business of airplay manipulation. Even if it doesn't, there is bound to be a big increase in the number of stations (local and national) offering opportunities for young musicians to get themselves heard.

The cake is getting bigger. And if you know what it's made of, a slice of it could soon be yours.