If today’s pop music has ever made you grouse about that damn noise on the radio, it’s not (just) because you’re getting older and grumpier. Music is actually getting louder. Sound engineers are tinkering with songs to make them stand out on the radio and on MP3s. Thus, pop charts have become the equivalent of an argument, where everyone keeps shouting louder and louder just to be heard.
This graph from NPR of the most prolific pop songs from 1979-2009 illustrates the point:
The basic tactic that sound engineers are employing is to turn the volume of every component on a track way up–from high frequencies to low. That way, the relative volume—basically the midpoint between the extremes–seems to remain the same. But the track sounds louder nonetheless.
The graph above shows that data: The different colored bands show the volumes of the various frequency bands; when stacked, they allow you to get a sense of how loud a song seems. (The composite value is something that sound engineers call RMS levels.)
A detail of some of the “songs” included on the chart: