Although it might not be obvious to the casual listener taking a spin through the radio dial, not all radio stations are created the same. Sure, they'll notice that different stations play different kinds of music, but it's more than that. In reality, across that dial, there are two distinct kinds of radio stations: commercial radio and non-commercial radio. From the perspective of a musician trying to get their songs played on the radio or a radio promotion company, the difference in these stations comes down to a lot more than formatting.
Non-commercial radio, also called non-comm for short, encompasses college radio and community based radio stations, including local NPR affiliates. Though these stations may carry advertising, it is widely spaced, unobtrusive and not the main source of station funding. Commercial radio, on the other hand, is just the opposite. The commercials are frequent and commercial breaks between songs may be quite long. Advertising is the source of the station budget on these stations.
Sounds pretty simple on the surface, right? For anyone doing a radio promotion campaign, these distinctions are significant. Why? Because non-commercial radio tends to have a lot more flexibility in their playlists and tends to be much more willing to play music from up and coming artists and non-mainstream artists than commercial radio - meaning it is usually the doorway through which up and coming musicians break into radio, and in fact, it may be the only sector of radio on which some genres of music get played regularly. These notions are especially true for indie musicians and musicians operating in niche genres.
Non-comm radio stations' flexibility comes from the fact that their funding isn't reliant solely (or at all) on advertising dollars. Although they certainly need listener numbers to keep their independent sources of funding, wherever they come from, they don't have to chase the kinds of ratings commercial radio stations need to show to advertisers to convince them to spend money with the station. That means that they can afford to take a chance on a new artist their listeners haven't heard of before. The scenario is a little bit chicken or egg - non-comm radio listeners tend to be the most open to new music of all radio audiences, and in fact, by playing new artists, non-comms are usually giving their audiences exactly what they want. However, because they don't need as large an audience as a commercial radio station does, they can afford to lose the listeners who do want to hear music by established artists they also encounter in national magazines, television, newspapers and tours. It's a self-reinforcing cycle that works in favor of indie music.
Non-commercial radio stations may also focus on niche genres of music. This is especially true of community radio stations, which may, for instance, only play jazz or folk music. This genre specific approach means that they have to delve deeper into a genre to fill up their playlist, which is good news for up and coming musicians in that genre looking for exposure. For some genres, non-comm radio may be their only outlet - and that's fine, because these are the stations fans of those genres turn to when they want radio.
In addition to playlist flexibility, non-comm radio is a great entry point for many musicians because there is less competition. Major labels tend to ignore non-comm entirely, which means radio promoters have an easier time getting the attention the radio staff and getting them to check out new promos.
The world of commercial radio is completely different. Commercial radio operates on the basis of ratings. They need to big listener numbers, and they need those numbers to be consistent, or indeed to be growing. These ratings are used by the station to demonstrate to potential advertisers that buying a commercial spot on the station will reach a significant number of people and is a worthwhile investment. These numbers are also used to price advertising. The more listeners a station has, the more they can charge for ad spots - and the more money they will have in their operating budget.
Because these stations need ratings so badly, they need to play music by musicians that can bring them those listeners. They therefore look for musicians with enough clout and budget to be reaching their listeners outside of radio. They want to play musicians that are getting major pieces of press - both nationally and in that radio station's market. They want musicians that are selling well in local record shops and nationally. They want to play music by musicians who are playing shows in that station's market. They want to play musicians who are advertising. Many up and coming musicians simply don't have the budget or the reach yet to meet the demands of commercial radio stations, so they are don't get played there are often as established artists do.
Radio promoters use these differences between non-comm radio and commercial radio to decide which stations to target for their artists. The other piece of the puzzle in choosing stations to promote to is radio markets. To brush up on market basics, check out What Are Radio Markets?.