Up indicates higher volume, and vice versa. Adjust the volume: Click and drag the line going through the center of the track.Once you have the music added to your video, here's how to start editing:

Finally, hit the red record button to start recording, and press it again to stop. Next, select your mic from the Input Source drop-down menu. Then click the microphone icon, located in the bottom-left corner of the video preview and select the Voiceover Options button (located to the right of the red record button). Lastly, if you want to record music or a voiceover from a microphone: Hook up your mic to your computer. Click and drag the desired track onto your project. If you want to add songs from a CD, insert your CD and then select Audio CD from the list of audio options. A Finder window will open, which you can use to select and add audio files from anywhere on your Mac. To add music files from anywhere on your computer, click File at the top of the screen, and then Import Media. If the music you want doesn't appear when you click Music, it might be saved somewhere that iMovie doesn't look by default.

How to fade out music in imovie