Because songs are recorded at different volumes and with different technologies over time, the volume that they play back at in iTunes can be different. This can be annoying – especially if you’ve just turned the volume up to hear a quiet song and the next one half deafens you.
Sound Check is a tool built into iTunes that scans your iTunes library and brings all songs to roughly an equal volume.
It does this by scanning the playback volume of songs in the library and adjusting the "normalization information" ID3 tag for the song. It does not change the original song file.
You can use Sound Check with both iTunes and the iPod. They require slightly different steps, though.
This feature is pretty cool, and is enable with just a few mouse clicks. Here’s how to use it with iTunes. (Learn how to use Sound Check with the iPod)
