System Configuration : Preferences : Editing Preferences : Fades Section

Fades Section
Crossfade Preview Pre-Roll
This setting specifies the amount of pre-roll to be added when you are auditioning crossfades in the Fades dialog.
Crossfade Preview Post-Roll
This setting specifies the amount of post-roll to be added when you are auditioning crossfades in the Fades dialog.
QuickPunch/TrackPunch Crossfade Length
Specifies a default length for crossfades created by QuickPunch or TrackPunch (Pro Tools HD and Pro Tools with Complete Production Toolkit only) recordings. Crossfades occur before the punch in and after the punch out.
Preserve Fades when Editing
This option preserves fade-ins and fade outs, and converts separated crossfades into corresponding fade-ins and fade-outs.
Default Fade Settings
Fade In
Selects the default envelope shape for fade-ins when using the Smart Tool.
Fade Out
Selects the default envelope shape for fade-outs when using the Smart Tool.
Crossfade
Selects the default envelope shape for crossfades when using the Smart Tool.
*
To apply a Fade In, Fade Out, or Crossfade to an Edit selection using the Default Fade settings, and without opening the Fades dialog, press Control+Start+F (Windows) or Command+Control+F (Mac).
REX
Selects the default envelope shape for fades and crossfades between clips (“slices”) in imported REX files.