If the start and loop start positions are different, you can choose which position should hit an upcoming quantize start point when you trigger a cell. This can be useful if the start position is set to an upbeat position, for example.
In Logic Pro, select one or more cells, click the disclosure arrow next to Play From in the Cell inspector, then choose one of the following settings from the Q Loop Start pop-up menu:
Off: The cell starts playing from the start position when the upcoming quantize start point is reached.
On: The cell starts playing as soon as possible, so that the loop start position is reached at the next upcoming quantize start position. Some content after the start position may be skipped.
On, Preserve Start: The cell always starts playing from the start position, so that the loop start position is reached at the upcoming or any following quantize start position. The cell may start later but plays all content between the start and loop start positions.
In Logic Pro, do one of the following:
Select one or more cells, then deselect the Loop checkbox in the Cell inspector.
Control-click a cell, then deselect Settings > Loop from the submenu.
Click the cycle area in the ruler of the Cell Editor.
The circular waveform in the cell changes to a linear shape. When the cell starts, it plays once to the end of the cell length, then stops (one-shot).
Choose View > Length as Position from the PDF
Logic Pro Instruments: PDF