Apple Soundtrack Pro 3 - Manual (Page 378)

When the slider is set to High, no thinning occurs. The envelope contains every movement
of the control. Dragging the slider to any position other than High results in some thinning
of envelope points. By default, the slider is set to a moderate amount of thinning.
For more information about Soundtrack Pro project preferences, see Project Preferences .
378 Chapter 15 Working with Automation