Apple Logic Pro 9 - Manual (Page 632)

You can also quantize sections of the same audio or MIDI region differently.
To quantize various parts of a region differently
1 Divide the region with the Scissors tool, and then use different quantization settings on
each segment—each new region.
2 Recombine the segments of the original region with the Glue tool.
This maintains the quantize values of each segment.
When you quantize audio, white lines are automatically added to the selected audio
regions. These white lines are called quantize flex markers—or simply quantize
markers—and their function is to correct the playback positions of transient markers
according to the setting chosen from the Quantize pop-up menu.
The quantization grid always begins at the start of a MIDI region. If the MIDI region does
not start at the beginning of a bar, neither does the quantization grid. If you alter the
start point of a MIDI region, you also alter the quantization grid.
632 Chapter 21 Quantizing Audio and MIDI