Playback and Recording : Audio Recording : Setting Punch and Loop Points : Timeline Selection Markers

Timeline Selection Markers
When tracks are record-enabled, Timeline Selection Markers for start and end times appear as red up and down arrows in the Main Timebase ruler. If no tracks are record-enabled, the Timeline Selection Markers are blue.
 
The Timeline Selection Markers can be moved, either separately or at the same time, to set record and play ranges.
To set the record range by dragging the Timeline Selection Markers:
1 If you want the Timeline Selection Markers to snap to the current Grid value, set the Edit mode to Grid
2 Drag the first Timeline Selection Marker (down arrow) to the start point of the range.
 
3 Drag the second Timeline Selection Marker (up arrow) to the end point of the range.
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If the current record range is already the right length and the range needs only to be moved to a new location, Option-drag (Mac) or Alt-drag (Windows) either Timeline Selection Marker to move both to a new location (while keeping the same length).