I don't expect a Haydn string quartet to make as much noise in my car as, say, Metallica. Some music is supposed to sound louder than other music. Would you please expand on this normalization concept a bit for me?

You're right, some music is supposed to sound louder than other music.

However, in the case of CDs, songs that are supposed to sound at the same volume might not be that way, depending on how the CD was mastered.

For instance, old CDs that were made in the heyday of vinyl don't push the dynamic range of the format very much. They were mastered for the dynamic range of LPs, and they don't get as loud as the CD will go. But new CDs do, because they've been mastered from the ground up with the CD format in mind. Compare any CD from the 80's to any CD created within the last few years. All the recent CDs are much louder, by more than just a few decibels.

This even applies when you're comparing the exact same song. For instance, you might have an old CD in your collection that's got the exact same song as a new remastered version of the album. The old CD will be MUCH quieter. Often, the songs get normalized when they create an artist's "greatest hits" album so that the songs fit together as a collection better.

Normalization isn't an issue for regular CD players because you'll tend to listen to one album at a time, and the whole album will be at its proper relative levels. But when you have something like the Empeg, you could be listening to a fifteen-year old track right before a recent track. What happens is that you turn up the volume for the old song, then when the new song starts, it's THIS F***ING LOUD and you have a heart attack scrambling for the volume control and hope that you didn't just blow your 200-dollar speakers.

Now, obviously this applies to pop music more than classical music. However, the same issues exist: older albums won't ever hit the peak levels on the CD, while new ones will. Remember that normalization doesn't just artificially make a song louder... the idea is that you measure the peaks in song, then you normalize the volume so that one song's peaks are pretty close to the same as the last one's. Even quiet songs can have loud peaks.

Radio stations have known this for years, and they use compressor/limiters to normalize their music. They also compress the audio to fit the dynamic range of FM radio, and to make the songs blend better with the commercials.

The Empeg, by its very nature, clearly shows how much difference there is in the mastering techniques from album to album. The equalization, compression, and overall volume of a CD will vary widely from album to album. That's why we need features like per-song EQ and normalization.