Command entry: Track View 
Utilities menu
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Track View Utilities
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Track View Utilities dialog
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Choose Soft Selection Settings Manager, then click OK.
Displays a toolbar with controls to adjust the range and falloff of the soft selection of keys in the Dope Sheet and Curve
Editor.
Interface
- Soft
-
Toggles usage of the soft selection. When this is off, only the selected keys are used, the soft selection is not.
- Range
-
Determines the range of keys affected by the soft selection.
- Falloff
-
Determines the distribution of the strength of the soft selection over the range of keys.