It's amazing what you can find in the help files
Rectified audio waveforms
In After Effects, audio waveforms are shown as "rectified" audio waveforms. This means that the magnitude of the audio is shown only in one direction from the horizontal axis on a logarithmic scale. This makes it easier to estimate the perception of the loudness of a sound.
You can switch back to the old method of showing audio waveforms by deselecting Rectified Audio Waveforms in the panel menu of the Timeline panel.
Where is the panel menu of the Timeline panel? Screenshot would be nice.
It is where it is in every panel. 3 little lines right near the name of the panel.