In country music, the melody-and-lyrics method is still the standard method of writing songs. (Nashville is in some respects the Brill Building’s spiritual home.) But in mainstream pop and R&B songwriting, track-and-hook has taken over, for several reasons. For one thing, track-and-hook is more conducive to factory-style song production. Producers can create batches of tracks all at one time, and then e-mail the MP3s around to different topliners. It is common practice for a producer to send the same track to multiple topliners—in extreme cases, as many as fifty—and choose the best melody from among the submissions. Track-and-hook also allows for specialization, which makes songwriting more of an assembly-line process. Different parts of the song can be farmed out to different specialists—verse writers, hook smiths, bridge makers, lyricists—which is another precedent established by Cheiron. It’s more like writing a TV show than writing a song. A single melody is often the work of multiple writers, who add on bits as the song develops. …In a track-and-hook song, the hook comes as soon as possible. Then the song ‘vamps’—progresses in three- or four-chord patterns with little or no variation. Because it is repetitive, the vamp requires more hooks: intro, verse, pre-chorus, chorus, and outro hooks. ‘It’s not enough to have one hook anymore,’ Jay Brown explains. ‘You’ve got to have a hook in the intro, a hook in the pre, a hook in the chorus, and a hook in the bridge, too.’ The reason, he went on, is that ‘people on average give a song seven seconds on the radio before they change the channel, and you got to hook them.’
— John Seabrook, The Song Machine: Inside the Hit Factory