Once upon a time, when pop was young and London swung, we were a nation of singles buyers. Albums provided a higher profit margin for the record companies, but it wasn't until the end of the 60s that the public started buying more albums than singles. Once they did though, that was that: LPs were the engine of the music industry, the focus of critical consideration. The fortunes of the album became an index of music's commercial and creative health.
Then, if the BPI's projections are right, singles sales will have topped 150m in 2009 – the most ever, up 400% in five years, and above albums for the first time in decades. Of course, there's no real cross-time comparison you can make: these days, any individual track counts as a "single" and they cost as little as 29p. Still, the singles boom is an inconvenient anomaly in current narratives of "what's happening to music". If you think recorded music is in terminal decline and should simply be a giveaway to support touring, you have to face the fact that millions seem happy to pay for it. But if you believe that recorded music is inherently valuable and its health has been sapped by piracy, you have to come to terms with the fact that the real value your paying audience attaches to a song is the same as a bag of crisps.
Clearly, things have changed since 1979, singles' analogue-era peak (when 89m were sold). But what's in flux isn't the popularity of music. The biggest-selling single of 2009, Lady Gaga's Poker Face, sold around as many copies as the top seller of 1968, Hey Jude. What nobody seems to have a handle on is the meaning of that popularity.
Pop music enjoys a dual existence as artform and as commercial product: the interplay between the two is part of what makes it so fascinating. Aesthetic choices made in a spirit of strict independence have a mass-appeal domino effect; gimmicks thought up by marketing cynics end up changing lives. So the meaning of music is intensely tied up in questions of distribution and price.
We know what expensive, scarce music means – each acquisition weighed, each record absorbed and explored. And we've learned what free music means – great playpen-libraries of MP3s, a giddy near-omniscience for listeners. What we don't know yet is what cheap music might mean: what happens when a song is worth less than a Pot Noodle.