Adding Other Sound
You can import sound, such as other interviews, music, and sound effects, to your podcast. Apple provides some music and effects in the Apple Loop menu. Or you can use your own audio. If you want to use your own sound files, you have two options.
1) Navigate to the file via the Media Browser. Important: to do this, you must first load your audio files into iTunes on the same computer.
If you don't see the Media browser, choose Control:Show Media Browser from the top menu, or press the Media Browser button, next to the Track Info button.
You will have to navigate to the sound file through iTunes in the Media Browser.
2) Drag a file into GarageBand. If you open a Finder window to the proper folder, you can drag a file directly into a GarageBand track.
Using the Apple Loop
GarageBand gives you the option of including built-in sound effects and music. Press the eye button in the lower left of the Timeline window. This takes you to the Apple Loop menu. You can navigate through different categories to find sound effects or music that are appropriate for your podcast. To add them to the mix, simply click and drag the file name to the timeline, and you can add it to an existing track or into a new track.
To return to the Editor view from the Apple Loop, press the button with the scissors on it, located next to the Loop Browser button with the eye icon.
Keep Tracks Organized
When you begin to add elements like these, organization is key.
Typically, your narration track should be kept at or near the top of the mix. Below that, keep any interview tracks. And below that keep the tracks with music and/or sound effects. The default tracks in GarageBand follow this pattern, with the music at the bottom and voices above that. At the top, Apple has placed the "Podcast" track, which contains the photos and video used in enhanced podcasts.
You can change the order of any track, except the Podcast track, by clicking and dragging the track head up or down.