Built-in Audio Editor

In the Design view select the audio you would like to edit by clicking on the speaker icon in the panel on top of the canvas. A drop down menu will show you a list of audio recordings in your scene, select the one you want to edit and click on the Pencil icon to open the Built-in Audio Editor.

To erase a part of the audio, use the cursor on the sound wave to click and highlight the part you want to erase (the play button will play the highlighted part only) and click X or press DEL.

Fade in and fade out, by just clicking the Fade in and Fade out icons you will execute a default fade in and fade out on your audio. To custom fade your audio, highlight the portion of the sound wave you want to fade. Click fade in or fade out to soften the audio, click it again to soften it more until you are satisfied. If you go too far you can use the undo button.

Use the different option tabs to adjust volume and insert silences (a silence will be inserted wherever you place the marker on the sound wave).