Talk of the Loudness Nation

I appeared on NPR's Talk of the Nation program today, chatting with host Neal Conen and fellow audio obsessives across this great land. The podcast is here if you're interested. But thinking back to what I said, I want to use this space to talk a little about the Loudness War, a subject on which I don't think I was as coherent as I could be. I devote a chapter to it in Perfecting Sound Forever, but for those who are new to the subject, here's a quick primer.

Beginning in the early '90s, CD's have been made to sound increasingly louder. A louder CD is one that sounds loud even if your volume is low. That sounds tautological, but one defining characteristic of loudness is that it is not an objective criteria. Case in point: It's pretty common to reach for the remote when a TV show goes to a commercial, because the commercial seems abrasively loud. But the signal the station is putting out probably has the same maximum peak at all times. The difference is that the peak is reached only sporadically during the programming, but almost incessantly during the commercial. By the same token, a classical radio station and a hip-hop radio station may be broadcasting at the same peak levels. But the classical station is hitting that peak once a minute, wheras the hip-hop station is reaching it every second. So the hip-hop station sounds louder.

Our ears perceive loudness based on average levels. The commercial and the hip-hop station, by hitting their peak more often, have a higher average level, so they sound louder, even if they aren't peaking any higher than the TV show or the classical station.

This is the psychoacoustic underpinning of what has come to be called the loudness war in CD mastering. Basically, mastering engineers take the music and compress its dynamic range, the difference between the softest and loudest parts of the signal. The average level of the music increases, and the music sounds louder.

To hear the loudness war in action, just load up your CD changer with discs that span the last 15 years or so, and play them on shuffle. You'll probably notice that you're constantly having to adjust the volume, increasing it for the older CD's and decreasing it for the newer ones.

I'll have more to say very soon about what this all means for the music we hear. But for now, watch this clip, which does a remarkably good job of summarizing the effects of dynamic range compression on music.