Even if you prefer your music in a certain format, there are times when stray file types find their way into your iTunes library. Perhaps a friend sends you one of his band’s new songs in a different format. One way to change a song’s format is to use iTunes’ built-in converter (Advanced➝Convert Selection To fileformat). The exact wording of the menu item depends on your iTunes import settings, which you can choose by selecting iTunes➝Preferences, going to the Advanced pane, and clicking on the Importing tab. If your Import Using pop-up menu is set to AAC Encoder, the item will read Convert Selection To AAC.
But this menu item has a couple more tricks up its sleeve. Suppose you saved your friend’s song to your desktop, and you want to import it into iTunes in the correct format. Simply hold down the alt key, then watch as the menu item (here, it’s Convert Selection To AAC) changes to Convert To AAC. Choosing this brings up a standard OS X file-selection dialog box; navigate to your music file and click on Open, and iTunes will convert the song to your preferred format while importing it into your iTunes library. The imported song is stored in your iTunes folder.
If you don’t want your converted song to end up in that folder, you can store it elsewhere. Using the file-selection dialog box to navigate to the song you want to convert, press and hold the alt key before clicking on the Open button. This brings up another file-selection box, allowing you to choose a new destination. The song will still end up in your iTunes library; it just won’t be stored in the default location.