Among the bevy of announcements during Steve Jobs's Macworld Expo keynote last week was the release of iTunes 3, a new version of Apple's free MP3-playing software that's available now, though only for Mac OS X.

<http://www.apple.com/itunes/>

New in iTunes 3 is Sound Check, a feature that normalizes playback volumes to avoid the situation where some tracks are shockingly louder or significantly softer than others. Although I hadn't noticed that much when I first started getting into MP3s, it's become increasingly annoying as my music collection grows. iTunes 3 also offers new categorization options that track the number of times each track has been played and let you rate each song from one to five stars. iTunes also records the last time each song was played.

The main new feature, though, is Smart Playlists, best thought of as filters for your music. For instance, you can create a rule that matches all songs in the Rock genre that were released during the 1960s, and iTunes automatically gathers together the appropriate songs. Even better, Smart Playlists update automatically, so if you add a new CD of early Beatles music, for instance, it will instantly appear in your 1960s Rock playlist. Smart Playlists become even more useful when combined with the play count and rating information, so you can, for instance, create a playlist that gives you 50 randomly selected electronic dance tracks you've rated more than four stars, 600 MB of blues songs recorded before 1970, or the 10 tracks you listen to most often. If you delete a song from a Smart Playlist that's limited to a specific number of songs or a specific size, iTunes automatically picks another appropriate song to fill the space.

iTunes 3 also now supports Audible.com, an Internet service from which you can purchase spoken word content for over 18,000 books, a variety of newspapers, and archived radio shows. With iTunes 3, you can set bookmarks to save your place in long audio books.

<http://www.apple.com/itunes/audiobooks.html>

Finally, iTunes 3 tries to help you regularize your MP3 collection by renaming the individual MP3 files in a regular fashion, a one-time action that wasn't entirely successful for me. Plus, a Consolidate Library command in the Advanced menu offers to move all the MP3 files that iTunes knows about into your Music folder.