On June 22, 1991, Billboard announced a new album had surpassed Out of Time, by R.E.M., to become the most popular in the country. It was Niggaz4life, by N.W.A., which had debuted the previous week at number 2 and sold nearly a million copies in its first seven days. Billboard had published an album chart for 45 years, but this marked a historic week: It was the first time that a rap group claimed the top spot on the Billboard 200.
It's something to reach back in time and take the temperature of astonished music critics in the early 1990s. Some contemporary music experts worried that hip-hop was one genre too many, and the diversity of pop music would shatter the very idea of a mainstream. David Samuels, writing in The New Republic in 1991, described rap to the magazine's readers as if it were a particularly complicated new entry in an officious encyclopedia:
"Hip-hop," the music behind the lyrics, which are "rapped," is a form of sonic bricolage with roots in "toasting," a style of making music by speaking over records. (For simplicity, I'll use the term "rap" interchangeably with "hip-hop" throughout this article.)
In the middle of the 20th century, Billboard started publishing the Hot 100, which lists the most popular songs in the country, and the Billboard 200, which does the same for albums. For decades, these lists were put together using methods that would offend even the most careless statistician, as I explained in "The Shazam Effect." Billboard had few ways to truly measure what albums were being sold in stores or played on the radio. Instead, they relied on an honor system, by asking record stores and DJs to self-report the most popular musicians of the moment. Both parties had reasons to lie, and not just because the labels would pressure radio stations and record stores to play the hand-picked hits.
Imagine, for example, that you're a record-store owner in the 1980s. You’ve just sold out of AC/DC, but you're still stocked with Bruce Springsteen albums. The honest thing to do would be to tell Billboard that AC/DC is the band of the moment. But the smart thing to do would be to tell Billboard that Bruce Springsteen is selling like crazy. That way, the Boss's album flies up the chart, which encourages fans of popular music to come back to the store and empty the shelves still holding his records.
So, for many years, Billboard wasn't a perfect mirror of American tastes. It was warped by label preferences and record-store inventories. It often over-counted songs that labels preferred (like rock) and under-counted genres they were indifferent toward (like country and rap).
But in 1991, this changed. First, Nielsen ended the record-store charade by releasing SoundScan, which used point-of-sales data from cash registers in stores. Finally, Nielsen had timely information on which albums were really selling. Around the same time, Billboard switched from trusting radio stations’ self-reports to monitoring airplay through a third party. The Hot 100 chart changed from a political document to a statistical register, honestly tracking the songs Americans were really buying and listening to.
But their most dramatic discovery fits with our story: In the early 1990s, rap and hip-hop emerged as, not only a mainstream sound, but the defining genre on the Billboard charts. As you can see in this, their rather awesome graph of the ebb and flow of music styles, no other mega-genre has been so dominant for so long.
One week after Billboard updated its chart methodology in 1991, the first rap album hit number one. For the next quarter-century, the British scientists found, the emergence of rap and hip-hop has proven to be more durable to the sound of pop music than even the dawn of classic rock. More than the British Invasion or the brief tyranny of 1980s drum-machines, Matthias Mauch said, 1991 was the most significant year in the history of pop music.