Tracks : Creating Tracks : Adding New Tracks by Double-Clicking in the Edit or Mix Windows : Audio Tracks
 
Audio Tracks
To add a new audio track of the same channel width as the last new track, do one of the following:
*Command-double-click (Mac) or Control-double-click (Windows) on the empty area of the Mix window below or to the right of any current tracks.
*Command-double-click (Mac) or Control-double-click (Windows) on the empty area of the Edit window below any current tracks.
If no tracks exist in the project, a stereo audio track is created by default.