Sound changes how a video feels, even when the picture stays exactly the same.

Watch the same ten seconds of video three times, silent, then with music, then with music and a voice. What changed?

1. No sound

2. Music

3. Music and a voice

Video: "Dublin snow benburb st", via Wikimedia Commons, free for anyone to use (CC0). The narrator is made up for this lesson.

Version 2 adds music and version 3 adds a voice over the music. Today you will edit one messy recording into a clean thirty-second music clip. Next lesson you will record your own voice over music, like version 3.

Almost every piece of digital media uses three kinds of sound, often at the same time. You heard two of them on the first step: music in version 2, and music with a voiceover in version 3.

• Voiceover is someone speaking to explain or tell the story, and it carries the information.
• Sound effects are short sounds like a door creaking or a notification. They make things feel real and show that something happened.
• Music is the background track, and it sets the mood before anyone says a word.

Think about the last short video you watched. Which of the three did you notice, and which did you not notice at all?

AudioMass is a free audio editor that runs in your browser. Open it at audiomass.co. Make sure the address ends in .co, because audiomass.com is a different site full of adverts.

Follow the steps below to open it and load the practice clip you downloaded. The green shape you will see is called a waveform, which is a picture of the sound. Tall parts are loud and flat parts are quiet.

The practice clip starts with about eight seconds of a creaking door before the music begins, and it goes on too long at the end. Neither part belongs in a finished clip.

Trimming takes two moves. First you select the part you do not want, and then you cut it. Everything after a cut slides left to fill the gap.