Editing : Fades and Crossfades : About Crossfades and Curves

About Crossfades and Curves
For more information, see the following topics:
To create a crossfade between two clips, use the Selector tool to select across the end point of the first clip and the start point of the second. The length of the selection determines the length of the crossfade. Though fades may appear to be discrete clips, they cannot actually be separated from the clips in which they were created. You can, however, create fade-ins and fade-outs for individual clips (see Creating Fades at the Beginnings and Ends of Clips).
Use the Fades dialog to select, view, and manipulate the curves used to perform fades and crossfades. Different volume curves can be assigned to the fade-out and fade-in portions of crossfades. The Fades dialog can also be used to audition a fade or crossfade before applying it.
The type of selection you make determines the character of the crossfade.
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Since crossfades are created by fading between overlapping audio material, a crossfade cannot be performed on clips that do not contain audio material beyond their clip boundaries.
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If a clip references insufficient data toexecute a selected fade or crossfade, you are prompted to either skip those fades or to adjust the bounds of the selection to execute those fades.