Click on the audio timeline, press the 'v' (volume) key and you'll see a blue line running the length of your audio track.
Double-click it 4 times, twice at the beginning and twice at the end of the desired location to add points.
Place your cursor between points 2 and 3 and drag them down to the bottom.
Drag points 2 & 3 over so that are right under points 1 & 4 respectively.
In the example below, I left points 2 and 3 up a bit so that you an see what I mean.
