Really interesting NY Times chart here showing the relative value of all units sold across different media (CD, vinyl, digital, etc) since 1978.

Does anyone know a similar breakdown by number of units sold (independent of value)?  It'd be interesting to see a breakdown of units (or even by tracks) to compare the total volume of legitimate songs being purchased over time.  I wonder if it's constant, or gradually increasing, or quickly increasing with the advent of the internet?

For example, if we could see that the number of songs both being produced and consumed is steadily increasing -- while simultaneously revenue is decreasing -- it seems hard to argue that revenue is correlated with increased song production/consumption.

(At best it could be argued that revenue leads to higher quality songs, but that's a tricky one given that "quality" is entirely subjective.)

And if revenue bears no correlation with song production/consumption, then policies that protect and maximize revenue (eg, Copyright) become rather difficult to defend given the stated purpose of music Copyright to -- essentially -- increase song production/consumption.

-david