Apple Logic Pro 8 Getting Started - Manual (Page 51)

Chapter 4 Editing MIDI Events 51
To quantize one or more selected notes:
1 Choose the Pointer tool, and select the notes by clicking, Shift-clicking, or rubber
banding.
2 Choose the desired quantization value in the Quantization menu at the top center of
the Piano Roll Editor.
You can also click the Quantize button to quantize selected events (with the value
chosen in the Quantization menu).
Quantization menu
Quantize button
Warning: Once you have quantized individual events in the Piano Roll Editor, you
should not use the Region Quantization parameter on the parent region. If you do
this, all individual event quantization changes will be lost.