This is a good little explanation of "compression." Which is squeezing music so that the loudest and softest portions are closer. Typically all sounds are made maximally loud.

Compression isn't utterly and completely evil--sometimes it does make things sound better. Nearly all radio stations use some compression on their audio (some purist classical stations don't), and many use WAY too much.

Unfortunately, a lot of record producers use way too much as well.

Here at WNMC we use just the right amount of compression, and we've had that verified by Goldilocks.