the edit tool

lets you edit the individual points that make a sound.

Click on a sound you wish to edit to make its points visible. You can also select sounds by rectangle selection like in the select tool. Next, you can:

click and drag on any handle to move the point to your liking.
remove a point by dragging it next to one of its neighbors. Of course, a sound cannot have less than two points.
add a point by clicking on any part of an already selected sound. You can click again to select it and move it.

In all cases, holding the shift key while dragging locks the current pitch. Dragging the selection when the pitch snap or time snap buttons are switched on will automatically make the dragged point snap to the current grid.