Editing : Edit Modes and Tools : Trim Tool

Trim Tool
With the Trim tool, you can quickly shorten or expand a clip (up to the entire length of the source audio file). The first time you trim a clip, Pro Tools automatically adds it to the Clip List as a new clip (with a name derived from the original) in order to differentiate it from the original.
The Trim tool is a nondestructive tool and does not actually modify the original audio or MIDI data (when working on clips). To return to the length of the original clip, drag it from the Clip List, or resize the edited clip with the Trim tool to its original length.
Use of the Trim tool is affected by the current Edit mode: Shuffle, Slip, Spot, or Grid (see Edit Modes).
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The Trim tool can also be used to lengthen and shorten MIDI notes (see Trimming Note Start and End Times), and also to scale automation and controller data up or down Drawing Automation.
To trim a clip with the Trim tool:
1 Select the Trim tool.
If necessary, do one of the following:
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– or – 
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Right-click on any track and select Tools > Trim Tools > Standard.
2 Move the cursor near the start or end of the clip, so the Trim Tool cursor appears.
 
To reverse the direction of the Trim tool, press Alt (Windows) or Option (Mac).
3 Do one of the following:
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– or – 
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When working with audio, you cannot trim past the boundaries of adjacent clips.
When trimming clips in a stereo or multichannel track, all channels are trimmed.
When using Shuffle mode, subsequent clips are slid as necessary to make room for the edited clip. If using Grid mode, the dragged start/end times snap to the nearest Grid boundary. If using Spot mode, the Spot dialog opens, where you can enter the new location for the clip’s start or end point.