Play the class the same ten seconds of video three times: silent, then with music, then with music and a voice over the top. Ask what changed.

Nothing on screen moved. The picture was identical every time. What changed was how it felt, and that is the job of audio.

Today you take one messy recording and turn it into a clean thirty second clip you could actually use in a project.

Almost every piece of digital media uses three kinds of sound, often at the same time.

• Voiceover. Someone speaking to explain or narrate. It carries the information.
• Sound effects. Short sounds like a door creak or a notification. They make things feel real and tell you something happened.
• Music. Background tracks. Music sets the mood before anyone has processed a single word.

Think about the last short video you watched. Which of the three did you notice, and which were you never aware of at all?

AudioMass is a free audio editor that runs in your browser. There is nothing to install and no account to make.

Follow the steps to open it and load a clip you can practise on. The green shape you end up looking at is a waveform, which is a picture of the sound: tall parts are loud, flat parts are quiet.

The sample clip opens with about ten seconds of a creaking door before the music starts, and it runs on too long at the end. Neither belongs in a finished piece.

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

A clip that starts at full volume sounds like a mistake, and one that stops dead sounds unfinished. A fade fixes both.

A fade in brings the sound up from silence over the first few seconds. A fade out takes it back down at the end. Watch the shape of the waveform change as you apply each one.