That's useful news, you say. It's important to us that we know what's on your Mp3 player while you wheeze around London in the rain.
But the half-thought-out, semi-theoretical upshot of that was this: rock 'n' roll imitates the sound of the era's technology, and at some level all music may always have done this.
Chuck Berry, Little Richard, early Stones and Beatles: the regular, metronomic pace of post-war industry and the sense that this is liberating rather than oppressive. Zeppelin and 1970s Stones: the sound of a finely tuned engine turning over. Sabbath, Stooges, Hawkwind, 1970s metal: crushed by the wheels of industry. Krautrock, acid and other psychonautical travellers: hunting for the ghosts within the machine.
Punk, post-punk, grunge-era dissonance and other experimental noise: the sound of spanners ricocheting around the works. Acid, techno, dance, electro and all their hydra-headed hybrids: regaining control of the machine and then willingly submitting to its will.
Ambient, illbient, drum 'n' bass and dubstep: music as information technology. Landfill indie and the limply neurotic rock which now soundtracks an afternoon trailing round the shops: semi-conscious nostalgia for a time when we knew where the machine was, what it was for and how to fix it when it was broken.