Sample Rounding and Edit Operations
When audio material in Pro Tools is sample-based, some amount of sample-rounding may occur with some edits when the Main Time Scale is set to Bars|Beats. This is most evident when you need audio clips to fall cleanly on the beat (as when looping) and notice that the material is sometimes a tick or two off. With a few simple precautions, this can be avoided.
To ensure that selections are precisely aligned to the grid for looping, copying, duplicating, or repeating, consider the following:
If you use the Selector tool, enable Grid mode and select the appropriate grid value (such as sixteenth notes).
For the greatest accuracy, type the selection Start and End points in the Event Edit area.
Do not select the material with any of the Grabber tools (or by double-clicking with the Selector tool).