You can then automate the volume of a track’s playback by clicking in the region, with the Grabber tool selected, to make new “breakpoints.” Dragging a breakpoint up or down adjusts the volume level of the track’s output — like turning a volume knob.
Option-click on a breakpoint to delete it (again with the Grabber). Drawing with the Pencil tool creates a dense stream of points that follows the line you draw freehand.
Selecting a range of points with the Selector tool allows you to delete or copy the selected volume automation. When a range of points is selected, the Trimmer tool can be used to raise or lower all selected points, preserving the shape of the volume envelop. Adjusting volume breakpoints simulates moving a track’s volume fader on a mixer.